Teach git-bundle to read revision arguments from stdin like git-rev-list.

Teach git-bundle to read revision arguments from stdin like git-rev-list.

This patch allows the caller to feed the revision parameters to git-bundle
from its standard input.  This way, a script do not have to worry about
limitation of the length of command line.

Documentation/git-bundle.txt says that git-bundle takes arguments acceptable
to git-rev-list.  Obviously some arguments that git-rev-list handles don't
make sense for git-bundle (e.g. --bisect) but --stdin is pretty reasonable.

Signed-off-by: Adam Brewster <adambrewster@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>