fix: only check for obsolete commits in the --rev case
With both `--all` and `--source`, we already exclude obsolete
revisions in the revset, so there's no need to call
`checkfixablectx()` in those cases.
Differential Revision: https://phab.mercurial-scm.org/D9227
#require serve
$ hg clone http://localhost:$HGPORT/ copy
abort: * (glob)
[255]
$ test -d copy
[1]
$ "$PYTHON" "$TESTDIR/dumbhttp.py" -p $HGPORT --pid dumb.pid
$ cat dumb.pid >> $DAEMON_PIDS
$ hg clone http://localhost:$HGPORT/foo copy2
abort: HTTP Error 404: * (glob)
[255]
$ killdaemons.py