profiling: flush stdout before writing profile to stderr
On py3, stdout and stderr appear to be buffered and this causes my command's
output to be intermixed with the profiling output.
Differential Revision: https://phab.mercurial-scm.org/D8024
cat >> $HGRCPATH <<EOF
[extensions]
narrow=
[ui]
ssh=python "$RUNTESTDIR/dummyssh"
[experimental]
changegroup3 = True
EOF