always resolve dependencies

at present if there's a lockfile all the dependencies from it are
returned, which blows at least :except (and probably :only) out of the
water. Now we'll try and use locked versions, but only after resolving
the groups we want.

Conflicts:
	lib/berkshelf/berksfile.rb
test that --except works with a lock file
remove lockfile sha support across the board

Conflicts:
	features/lockfile.feature
	features/update_command.feature
	lib/berkshelf/berksfile.rb
	lib/berkshelf/lockfile.rb
	spec/fixtures/cookbooks/example_cookbook/Berksfile.lock
	spec/unit/berkshelf/berksfile_spec.rb
	spec/unit/berkshelf/lockfile_spec.rb
clobber extraneous newline
Lockfile#update no longer needs an options arg

Conflicts:
	lib/berkshelf/lockfile.rb
update comment on locking algorithm
fix up whitespace a touch
Missed one