rebase: sort destmap topologically
Previously rebase source and destination could not overlap. But with the
multi-destination support, source and destination could reasonably partially
overlap. That requires another topological sort on `{sourcerev: destrev}`
graph (destmap). This patch implements that.
If a revision's destination is itself, the error message gets changed from
"source is ancestor of destination" to "source and destination form a
cycle". Not marking as BC since automation should depend on exit code, not
error message.
Differential Revision: https://phab.mercurial-scm.org/D470
$ hg init
$ echo 123 > a
$ hg add a
$ hg commit -m "first" a
$ mkdir sub
$ echo 321 > sub/b
$ hg add sub/b
$ hg commit -m "second" sub/b
$ cat sub/b
321
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cat sub/b 2>/dev/null || echo "sub/b not present"
sub/b not present
$ test -d sub || echo "sub not present"
sub not present