revlog: speed up prefix matching against nodes
The radix tree already contains all the information we need to
determine whether a short string is an unambiguous node identifier.
We now make use of this information.
In a kernel tree, this improves the performance of
"hg log -q -r
24bf01de75" from 0.27 seconds to 0.06.
Issue351: mq: qrefresh can create extra revlog entry
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ hg qinit
$ echo b > b
$ hg ci -A -m foo
adding b
$ echo cc > b
$ hg qnew -f foo.diff
$ echo b > b
$ hg qrefresh
$ hg debugindex b
rev offset length base linkrev nodeid p1 p2
0 0 3 0 0 1e88685f5dde 000000000000 000000000000