cat: default to working dir parent instead of tip This introduces a defaultrev function that chooses the working dir parent if a revision isn't specified, and uses it in several places.

#!/bin/sh

unset HGUSER
EMAIL="My Name <myname@example.com>"
export EMAIL

hg init test
cd test
touch asdf
hg add asdf
hg commit -d '1000000 0' -m commit-1
hg tip