Teach bash completion about recent log long options

Teach bash completion about recent log long options

(Somewhat) recently git-log learned about --reverse (to show commits
in the opposite order) and a looong time ago I think it learned
about --raw (to show the raw diff, rather than a unified diff).
These are both useful options, so we should make them easy for the
user to complete.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>