Some systems show "Thu Jan 01" instead of "Thu Jan 1", which breaks tests.
Using "1000000" yields "Mon Jan 12 13:46:40 1970", which looks the same on
all systems.
When the destination of a copy or rename operation has been
marked for removal, we need to restore it before we overwrite
it with the new content. This also handles the case of
idempotent renames, i.e.
hg rename "a" "b"
hg rename "b" "a"
Add support for transitive copy or rename operations, e.g.
hg rename a b
... (possibly edit b)
hg rename b c
hg commit ...
by actually renaming "b" as "c" while recording a copy of
"a" to "c" and a removal of "a".
