hook: flush stdout before redirecting to stderr stable

hook: flush stdout before redirecting to stderr

When hook output redirection is enabled (e.g. when cloning over ssh), hook
output on stdout is redirected to stderr, to prevent the repository data on
stdout from being corrupted.
In certain cases, the redirection could cause part of the repository data to
end up on stderr as well. In case of a clone, this causes:
"abort: consistency error in delta!"

This was seen with a clone over ssh, an outgoing hook present (any
non-python type, e.g. 'pwd'), on certain repositories only,
probably depending on the distribution of the sent data)

This patch updates the hook redirection code to flush stdout before
redirecting, removing the problem.

--- a/mercurial/hook.py	Wed Nov 16 12:53:10 2011 +0100
+++ b/mercurial/hook.py	Wed Nov 16 08:34:36 2011 +0100
@@ -139,6 +139,7 @@
             stderrno = sys.__stderr__.fileno()
             # temporarily redirect stdout to stderr, if possible
             if stdoutno >= 0 and stderrno >= 0:
+                sys.__stdout__.flush()
                 oldstdout = os.dup(stdoutno)
                 os.dup2(stderrno, stdoutno)
         except AttributeError: