keyword: lowercase status flags of untracked files in kwfile output Document the flags and their meanings in the command help (thanks to timeless for bringing this to my attention).

help: branch heads have no descendants, not no children

Branch heads should not include "heads" that are ancestors of other heads. For example, given 1 (branch a) -> 2 (branch b) -> 3 (branch a) I expect "hg heads a" to show only 3. Discovered by running hg heads HEAD on the mutt repo, where older clients committed default on top of HEAD.