revisions: when using prefixhexnode, ensure we prefix "0"
Previously, if using `experimental.revisions.disambiguatewithin` (and it didn't
include rev0), and '0' was the shortest identifier in that disambiguation set,
we printed it as the shortest *without* a prefix. This was because we had logic
to determine "if the prefix is a pure integer, but starts with 0, we don't need
to prefix with 'x': 01 is not a synonym for revision #1", but didn't handle the
case where prefix == 0 (which is a pure integer, and starts with 0... but it
*is* "rev0").
Differential Revision: https://phab.mercurial-scm.org/D5113
#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