[PATCH 2 of 2 V2] dispatch: flush ui before returning from _runcatch

[Jun Wu]

# HG changeset patch
# User Jun Wu <quark at fb.com>
# Date 1457953594 0
#      Mon Mar 14 11:06:34 2016 +0000
# Node ID 40b571e817902d930d1d828769d2d29bbba88de1
# Parent  37c1410031153c71a46a467e6c94af16a7266d02
dispatch: flush ui before returning from _runcatch

A chg client may exit after received the result from runcommand. It is
necessary to do a flush to make sure the warning message is printed out
and the process waiting for the chg client will actually see the output.

This helps chg to pass test-alias.t.

diff --git a/mercurial/dispatch.py b/mercurial/dispatch.py
--- a/mercurial/dispatch.py
+++ b/mercurial/dispatch.py
@@ -384,6 +384,7 @@
         ui.warn(warning)
         raise
 
+    ui.flush()
     return -1
 
 def aliasargs(fn, givenargs):