rebase: sort destmap topologically...
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
