merge: make test for fast-forward merge stricter (issue619)
don't allow merging with an ancestor
fix != on contexts
add a test
#!/bin/sh
mkdir t
cd t
hg init
echo a > a
hg ci -Ama -d '1000000000 0'
echo b > b
hg branch b
hg ci -Amb -d '1000000000 0'
hg co -C 0
echo fast-forward
hg merge b
hg ci -Ammerge -d '1000000000 0'
echo bogus fast-forward should fail
hg merge b
echo done