maint: doc and maintainer-check in preparation for 1.17.90.

* HACKING: mention thanks to individuals.
* NEWS: update for 1.17.90.
* configure.ac (AC_INIT): now 1.17.90.
* m4/amversion.m4 (AM_AUTOMAKE_VERSION): 1.17.90 (auto-update).
* maintainer/syntax-checks.mk (sc_tests_command_subst): allow
whitespace before # shell comment line.
(sc_tests_plain_sleep): emphasize using $sleep without a number;
only replace sleep 1 or sleep 2; longer than that would be fine.
* t/tap-stderr-prefix.tap: use $sleep instead of sleep 1.
diff --git a/HACKING b/HACKING
index 78401fa..1b39d7c 100644
--- a/HACKING
+++ b/HACKING
@@ -551,14 +551,17 @@
   version number schemes. The test t/pm/Version[.pl] comprehensively
   checks valid and invalid version strings.
 
-* If making a minor or major release (1.x), also update APIVERSION
-  in configure.ac. But not micro.
+* If making a minor or major release (1.x), also update APIVERSION in
+  configure.ac. But not micro. Don't change APIVERSION for pretests,
+  e.g., APIVERSION=1.17 for the pretest 1.17.90, even though it's
+  leading up to 1.18.
 
 * Create an announcement message with "make announcement".  Edit the
   generated 'announcement' file appropriately, in particularly filling
-  in by hand any "TODO" left in there.  It's useful to do this early,
-  because carefully writing the announcement can easily bring to light
-  things that still need to be worked on.
+  in by hand any "TODO" left in there.  In particular, thank people who
+  should be thanked (read through the ChangeLog).  It's useful to do
+  this early, because carefully writing the announcement can easily
+  bring to light things that still need to be worked on.
 
 * Run these commands, in this order (as mentioned, adjust -j as desired):
     make bootstrap
@@ -574,8 +577,15 @@
   because that command will remove *all* the files that are not tracked
   by git!  Run git status first to ensure all removals are ok.
 
+* Run "make git-tag-release".
+  This will run the maintainer checks, verify that the local git
+  repository and working tree are clean and up-to-date, and create
+  a proper signed git tag for the release (based on the contents
+  of $(VERSION)).
+
 * Create additional info for the announcement with the announce-gen
-  script that is part of gnulib (it requires the release tarball):
+  script that is part of gnulib.  It requires the new release tarball,
+  and the repository to be tagged
     pkg=automake
     prever=1.16.92
     newver=1.16.94
@@ -588,12 +598,6 @@
       --url-directory=https://$host.gnu.org/gnu/$pkg
   and merge this with the just-written announcement file.
 
-* Run "make git-tag-release".
-  This will run the maintainer checks, verify that the local git
-  repository and working tree are clean and up-to-date, and create
-  a proper signed git tag for the release (based on the contents
-  of $(VERSION)).
-
 * Run "make git-upload-release".
   For pretest releases: "DEVEL_SNAPSHOT=1 make git-upload-release".
 
diff --git a/NEWS b/NEWS
index 9c1b568..f46191a 100644
--- a/NEWS
+++ b/NEWS
@@ -2,7 +2,7 @@
 please see NEWS-future and start following the advice there now.
 
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-New in 1.x:
+New in 1.17.90:
 
 * New features added
 
diff --git a/configure.ac b/configure.ac
index 27fe4a3..0b1afda 100644
--- a/configure.ac
+++ b/configure.ac
@@ -16,7 +16,7 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 AC_PREREQ([2.69])
-AC_INIT([GNU Automake], [1.17.0.91], [bug-automake@gnu.org])
+AC_INIT([GNU Automake], [1.17.90], [bug-automake@gnu.org])
 
 AC_CONFIG_SRCDIR([bin/automake.in])
 AC_CONFIG_AUX_DIR([lib])
diff --git a/m4/amversion.m4 b/m4/amversion.m4
index c7a6e81..a3bfe9b 100644
--- a/m4/amversion.m4
+++ b/m4/amversion.m4
@@ -15,7 +15,7 @@
 [am__api_version='1.17'
 dnl Some users find AM_AUTOMAKE_VERSION and mistake it for a way to
 dnl require some minimum version.  Point them to the right macro.
-m4_if([$1], [1.17.0.91], [],
+m4_if([$1], [1.17.90], [],
       [AC_FATAL([Do not call $0, use AM_INIT_AUTOMAKE([$1]).])])dnl
 ])
 
@@ -31,7 +31,7 @@
 # Call AM_AUTOMAKE_VERSION and AM_AUTOMAKE_VERSION so they can be traced.
 # This function is AC_REQUIREd by AM_INIT_AUTOMAKE.
 AC_DEFUN([AM_SET_CURRENT_AUTOMAKE_VERSION],
-[AM_AUTOMAKE_VERSION([1.17.0.91])dnl
+[AM_AUTOMAKE_VERSION([1.17.90])dnl
 m4_ifndef([AC_AUTOCONF_VERSION],
   [m4_copy([m4_PACKAGE_VERSION], [AC_AUTOCONF_VERSION])])dnl
 _AM_AUTOCONF_VERSION(m4_defn([AC_AUTOCONF_VERSION]))])
diff --git a/maintainer/syntax-checks.mk b/maintainer/syntax-checks.mk
index 00c62fb..01918a8 100644
--- a/maintainer/syntax-checks.mk
+++ b/maintainer/syntax-checks.mk
@@ -335,7 +335,7 @@
 sc_tests_command_subst:
 	@found=false; \
 	scan () { \
-	  sed -n -e '/^#/d' \
+	  sed -n -e '/^ *#/d' \
 	         -e '/<<.*END/,/^END/b' -e '/<<.*EOF/,/^EOF/b' \
 	         -e 's/\\`/\\{backtick}/' \
 	         -e "s/[^\\]'\([^']*\`[^']*\)*'/'{quoted-text}'/g" \
@@ -446,8 +446,8 @@
 # a 2sec resolution.
 sc_tests_plain_sleep:
 	@if grep -vE '^[ 	]*#' $(xtests) \
-	      | grep -E '\bsleep +[12345]\b' | grep .; then \
-	  echo 'Do not use "sleep x" in the above tests.  Use "$$sleep" instead.' 1>&2; \
+	      | grep -E '\bsleep +[12]\b' | grep .; then \
+	  echo 'Do not use "sleep x" in the above tests; use "$$sleep" (no x).' 1>&2; \
 	  exit 1; \
 	fi
 
diff --git a/t/tap-stderr-prefix.tap b/t/tap-stderr-prefix.tap
index 7f2ea24..ce00e1d 100644
--- a/t/tap-stderr-prefix.tap
+++ b/t/tap-stderr-prefix.tap
@@ -136,11 +136,11 @@
 cat >all.test <<END || bailout_ "failed to create all.test"
 #!/bin/sh
 echo '1..1'
-sleep 1
+$sleep
 echo 'stderr 1' >&2
-sleep 1
+$sleep
 echo 'ok 1'
-sleep 1
+$sleep
 echo 'stderr 2' >&2
 END
 chmod a+x all.test || bailout_ "failed to make all.test executable"