blackbox: adds a 'blackbox' command for viewing recent logs
Adds a 'hg blackbox' command for viewing the latest entries in the blackbox log.
By default it shows the last 10 entries, but -l allows the user to specify.
$ 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