merge: when current branch has 1 or > 2 heads, actually abort.
Currently merge just prints abort-like messages to stderr and then
exits with a misleading status 0 (cleverly disguised as "False").
With this change it raises Abort, just like every other fatal error.
#!/bin/sh
hg init test
cd test
cat > .hg/hgrc <<EOF
[server]
validate=1
EOF
echo alpha > alpha
echo beta > beta
hg addr
hg ci -m 1
cd ..
hg clone test test-clone
cd test-clone
cp .hg/store/data/beta.i tmp
echo blah >> beta
hg ci -m '2 (corrupt)'
mv tmp .hg/store/data/beta.i
hg push 2>&1 | "$TESTDIR/filtertmp.py"