prepush: add more precise error messages
Part of the patch is from timeless@mozdev.org
- indicate the branch name where there are multiple heads
- give better advice when hitting a possible race, where new heads are added
between discovery and the call to branchmap(). In that case, asking the user
to merge isn't helpful, since only remote has the changes.
adding b
rev offset length base linkrev nodeid p1 p2
0 0 3 0 0 1e88685f5dde 000000000000 000000000000