Fix flush for sys.stderr

GDB overwrites Python's sys.stdout and sys.stderr, but does not
properly implement the 'flush' method -- it only ever will flush
stdout.  This patch fixes the bug.  I couldn't find a straightforward
way to write a test for this.

gdb/python/lib/gdb/__init__.py

diff --git a/gdb/python/lib/gdb/__init__.py b/gdb/python/lib/gdb/__init__.py
index 5b10e3e..191915e 100644
--- a/gdb/python/lib/gdb/__init__.py
+++ b/gdb/python/lib/gdb/__init__.py
@@ -39,6 +39,9 @@
     encoding = "UTF-8"
     errors = "strict"
 
+    def __init__(self, stream):
+        self.stream = stream
+
     def close(self):
         # Do nothing.
         return None
@@ -51,23 +54,15 @@
             self.write(line)
 
     def flush(self):
-        flush()
+        flush(stream=self.stream)
 
-
-class _GdbOutputFile(_GdbFile):
     def write(self, s):
-        write(s, stream=STDOUT)
+        write(s, stream=self.stream)
 
 
-sys.stdout = _GdbOutputFile()
+sys.stdout = _GdbFile(STDOUT)
 
-
-class _GdbOutputErrorFile(_GdbFile):
-    def write(self, s):
-        write(s, stream=STDERR)
-
-
-sys.stderr = _GdbOutputErrorFile()
+sys.stderr = _GdbFile(STDERR)
 
 # Default prompt hook does nothing.
 prompt_hook = None

gdb/testsuite/gdb.python/python.exp

diff --git a/gdb/testsuite/gdb.python/python.exp b/gdb/testsuite/gdb.python/python.exp
index 8c0da6d..48ff07e 100644
--- a/gdb/testsuite/gdb.python/python.exp
+++ b/gdb/testsuite/gdb.python/python.exp
@@ -297,8 +297,8 @@
 }
 
 # gdb.write
-gdb_test "python print (sys.stderr)" ".*gdb._GdbOutputErrorFile (instance|object) at.*" "test stderr location"
-gdb_test "python print (sys.stdout)" ".*gdb._GdbOutputFile (instance|object) at.*" "test stdout location"
+gdb_test "python print (sys.stderr)" ".*gdb._GdbFile (instance|object) at.*" "test stderr location"
+gdb_test "python print (sys.stdout)" ".*gdb._GdbFile (instance|object) at.*" "test stdout location"
 gdb_test "python gdb.write(\"Foo\\n\")" "Foo" "test default write"
 gdb_test "python gdb.write(\"Error stream\\n\", stream=gdb.STDERR)" "Error stream" "test stderr write"
 gdb_test "python gdb.write(\"Normal stream\\n\", stream=gdb.STDOUT)" "Normal stream" "test stdout write"