Split init_revisions() out of setup_revisions()

Split init_revisions() out of setup_revisions()

Merging all three option parsers related to whatchanged is
unarguably the right thing, but the fallout was too big to scare
me away.  Let's try it once again, but once step at time.

This splits out init_revisions() call from setup_revisions(), so
that the callers can set different defaults to match the
traditional benaviour.

The rev-list command is still broken in a big way, which is the
topic of next step.

Signed-off-by: Junio C Hamano <junkio@cox.net>