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

changeset:   0:9426b370c206
tag:         tip
user:        My Name <myname@example.com>
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     commit-1

changeset:   1:4997f15a1b24
tag:         tip
user:        foo@bar.com
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     commit-1

changeset:   2:72b8012b424e
tag:         tip
user:        foobar <foo@bar.com>
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     commit-1

changeset:   3:35ff3067bedd
tag:         tip
user:        foo@bar.com
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     commit-1

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