Move the logic to read revs from standard input that rev-list knows about
from it to revision machinery, so that all the users of setup_revisions()
can feed the list of revs from the standard input when "--stdin" is used
on the command line.

Allow some users of the revision machinery that want different semantics
from the "--stdin" option to disable it by setting an option in the
rev_info structure.

This also cleans up the kludge made to bundle.c via cut and paste.

Signed-off-by: Junio C Hamano <gitster@pobox.com>