hgmerge: logic changes
Details:
- keep automatic merge conflicts in $LOCAL
- do not assume that $EDITOR returns proper error code
- fix a slight mistake in diff+patch merge success detection
(it could succeed if the $EDITOR failed to run)
abort: Failed to parse .../t/.hg/hgrc
File contains no section headers.
file: .../t/.hg/hgrc, line: 1
'invalid\n'