prepush: fix bug in warning message selection
In certain situations you would be told "you should pull and merge" even when
there is nothing to pull.
#! /bin/sh
# issue 1678
echo "# -- setting up base repo"
hg init a
cd a
touch a
hg ci -Am a
cd ..
echo "# -- cloning base repo"
hg clone a b
cd b
echo "# -- setting up cset to push"
hg up null
touch a
hg ci -Am b # different msg so we get a clog new entry
echo "# -- pushing"
hg push -f ../a