fix dupe detection with similar-looking-but-not-the-same repo paths

with -r, exclude test deps of dependencies

add tag support and -x for excluding tags

push dependency fetch optimization into Fetcher

implement 'bleeding-edge' dependencies

remove -a help text (no longer exists)

dependency fetcher -> fetcher

refactor dependency set management into Set object

remove -a (aggregate) functionality

remove gocart symlink

refactory repository logic into a better interface

remove -t, -r now does depth-first

improve 'gocart check' output

Favor displaying dirty repos over mismatched shas

simplify check test (maybe fix travis)