Replace backslashes by forward slashes in paths canonicalization

* tta/C/main/utils.c (file_separator_canonpath): rename canonpath as
file_separator_canonpath and modify to put only forward slash in
output file name.  Update callers.

* tta/perl/Texinfo/Common.pm (file_separator_canonpath),
tta/perl/Texinfo/Convert/Converter.pm (determine_files_and_directory),
tta/perl/Texinfo/Convert/Text.pm (output), tta/perl/texi2any.pl: add
file_separator_canonpath as a wrapper around File::Spec->canonpath
that replace backslashes by forward slashes on Windows.  Report and
analysis from Eli Zaretskii.
10 files changed