bundle2: rename unbundle2 test command to statbundle2
We will introduce object to actually process the bundle, we need to keep the
simplistic unbundle around for the test.
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state