version: add --brief flag

This prints the version only, which the maintainer scripts use.

Signed-off-by: David Aguilar <davvid@gmail.com>
.gitignore: add zip and tar

Signed-off-by: David Aguilar <davvid@gmail.com>
Makefile: fix "make dist" target

It was broken when we reworked the sub-commands, and now uses:

	git-cola version --brief

Signed-off-by: David Aguilar <davvid@gmail.com>
git-cola v1.9.1

Signed-off-by: David Aguilar <davvid@gmail.com>