graphlog: fix --follow --rev combinations
The previous behaviour of --follow was really a subset of what is really
happening in log command:
- If --rev is not passed, default to '.:0'
- Resolve --rev into a revision list "revs"
- Set the starting revision to revs[0]
- If revs[1] > revs[0] keep descendants(revs[0]) in revs, otherwise keep
ancestors.
Minimal hgk check
$ echo "[extensions]" >> $HGRCPATH
$ echo "hgk=" >> $HGRCPATH
$ hg init repo
$ cd repo
$ echo a > a
$ hg ci -Am adda
adding a
$ hg debug-cat-file commit 0
tree a0c8bcbbb45c
parent 000000000000
author test 0 0
committer test 0 0
revision 0
branch default
adda