Fixup long-missing pants_exe and goal deps exposed by a cleanup of other deps.

Testing Done:
Travis CI away here: https://travis-ci.org/pantsbuild/pants/builds/30806546
Local test kept timing out on package downloads.

Bugs closed: 393

Reviewed at https://rbcommons.com/s/twitter/r/745/
Update contributors guide for rbt fixes

Account for the closed `rbt` bug in the contributors guide.

Reviewed at https://rbcommons.com/s/twitter/r/738/
revert
Merge branch 'master' into lahosken_pagetree
merge and a cargo-cult change