simplemerge: flush stdout before writing to stderr.
Besides, stderr is not always unbuffered under win32 (when redirections occur for instance), and it should be flushed too.
adding a
adding b
copy .hg/patches to .hg/patches.1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
M b
a
b
merging with queue at: .hg/patches.1
applying rm_a
Now at: rm_a
b