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

abort: file .../test-symlink-basic/a/dangling not tracked!
changeset:   0:cabd88b706fc
tag:         tip
user:        test
date:        Thu Jan 01 00:00:00 1970 +0000
files:       dangling
description:
add symlink


2564acbe54bbbedfbf608479340b359f04597f80 644 dangling
% rev 0:
dangling -> nothing
% rev 1:
dangling -> void
% modifying link
dangling -> empty
% reverting to rev 0:
reverting dangling
dangling -> nothing
% backups:
dangling.orig -> empty
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
% copies
copying dangling to dangling2
A dangling2
  dangling
dangling -> void
dangling2 -> void