merge: better error messages to lead users to hg update --clean to abandon merges.
Fixes
issue1533.
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
created new head
% Merging a conflict araises
merging A
warning: conflicts during merge.
merging A failed!
1 files updated, 0 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges or 'hg up --clean' to abandon
% Correct the conflict without marking the file as resolved
abort: unresolved merge conflicts (see hg resolve)
% Mark the conflict as resolved and commit