revlist.c: introduce --left/right-only for unsymmetric picking

revlist.c: introduce --left/right-only for unsymmetric picking

The existing "--cherry-pick" does not work with unsymmetric ranges
(A..B) for obvious reasons.

Introduce "--left-only" and "--right-only" which limit the output to
commits on the respective sides of a symmetric range (i.e. only "<"
resp. ">" commits as per "--left-right").

This is especially useful for things like

    git log --cherry-pick --right-only @{u}...

which is much more flexible (and descriptive) than

    git cherry @{u} | sed -ne 's/^+ //p'

and potentially more useful than

    git log --cherry-pick @{u}...

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>