rebase: calculate obsolescense-related info earlier...
rebase: calculate obsolescense-related info earlier
My goal is to use `rewriteutil.precheck()` in the rebase code. Since
rebase does its own handling of divergent commits (it skips them
instead of erroring out), we need to have divergence-causing commits
filtered out early. This patch helps prepare for that.
Differential Revision:
https://phab.mercurial-scm.org/D10247