tests/test-merge9.out

prepush: add more precise error messages

Part of the patch is from [e-mail]

- 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 bar
adding foo
adding quux1
adding quux2
created new head
merging bar
merging bar failed!
merging foo and baz to baz
1 files updated, 1 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges or 'hg update -C' to abandon
U bar
R baz
3 files updated, 0 files merged, 1 files removed, 0 files unresolved
merging bar
merging bar failed!
merging baz and foo to baz
1 files updated, 1 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges or 'hg update -C' to abandon
% show unresolved
U bar
R baz
% unmark baz
% show
U bar
U baz
M bar
M baz
M quux2
? bar.orig
% re-resolve baz
merging baz and foo to baz
% after
U bar
R baz
% resolve all warning
abort: no files or directories specified; use --all to remerge all files
% resolve all
merging bar
warning: conflicts during merge.
merging bar failed!
% after
U bar
R baz