merge: do early copy to deal with issue636 Without copies/renames, merges source names are 1:1 with their targets. Copies and renames introduce the possibility that there will be two merges with the same input but different output. By doing the copy to the destination name before the merge, the actual merge becomes 1:1 again, and no source is the input to two different merges. - add a preliminary scan to applyupdates to do copies - for the merge action, pass the old name (for finding ancestors) and the new name (for input to the merge) to filemerge - eliminate the old post-merge copy - lookup file contents from new name in filemerge - pass new name to external merge helper - report merge failure at new name - add a test

adding bar
adding foo
adding quux1
adding quux2
merging bar
merging bar failed!
merging foo and baz
merging baz failed!
1 files updated, 0 files merged, 0 files removed, 2 files unresolved
There are unresolved merges, you can redo the full merge using:
  hg update -C 2
  hg merge 1
3 files updated, 0 files merged, 1 files removed, 0 files unresolved
merging bar
merging bar failed!
merging baz and foo
merging baz failed!
1 files updated, 0 files merged, 0 files removed, 2 files unresolved
There are unresolved merges, you can redo the full merge using:
  hg update -C 1
  hg merge 2