Add branchtags function with cache - cache stores tipmost node and rev and node,label pairs - if cache is out of date, scan new changesets - write new cache out after scan

#!/bin/sh

hg init
python -c 'print "confuse str.splitlines\nembedded\rnewline"' > a
hg ci -Ama -d '1 0'
echo clean diff >> a
hg ci -mb -d '2 0'
hg diff -r0 -r1