phases: use revision number in `_pushdiscoveryphase`
We now reach our target checkpoint in terms of rev-num conversion. The
`_pushdiscoveryphase` function is now performing graph computation based on
revision number only. Avoiding repeated conversion from node-id to rev-num.
See previous changeset updated `new_heads` for rationnal.
Again, time saved in the 100 milliseconds order of magnitude for the mozilla-try
benchmark I have been using.
However, wow that the logic is done using revision number, we can look into having
better logic in the next changesets, which will provide a much bigger speedup.
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init repo
$ cd repo
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state