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
foo renamed from bar:26d3ca0dfd18e44d796b564e38dd173c9668d3a9
rev offset length base linkrev nodeid p1 p2
0 0 6 0 0 26d3ca0dfd18 000000000000 000000000000
1 6 7 1 1 d267bddd54f7 26d3ca0dfd18 000000000000