Move various build graph-related files to new pkg: build_graph.

Review Request #2899 - Created Sept. 28, 2015 and submitted

Benjy Weinberger
jsirois, kwlzn, mateor, zundel

pants/base was getting crowded. Moving this will make it somewhat
easier to later refactor/reimplement aspects of BUILD file parsing.

Note: doesn't move some core files like target and payload, as those
are heavily referenced in plugins. A followup change *may* move
those, but with a proper deprecation cycle.

After this change there are no dependencies from base to build_graph.
Target does take a build_graph argument (but doesn't reference
the type explicitly).

Also moves cache_manager/build_invalidator to a new pants/invalidation
package, as this helped untangle weird deps.

Note to Foursquare people: This will break a couple of our internal
plugins, which will need to move their imports of VersionedTargetSet.

CI passes:

Stu Hood
Benjy Weinberger
Benjy Weinberger
Kris Wilson
Eric Ayers
Eric Ayers
Benjy Weinberger
Review request changed

Status: Closed (submitted)

Change Summary:


Benjy Weinberger

Thanks folks! Submitted as 9e0d1bb6df96077d32587eb941ff9bcb16fc12d5.

Mateo Rodriguez
Ship It!