Refactor BUILD file parsing
Refactor BUILD file parsing

* Shuffle around some modules to reduce circular imports
* Move is_jvm, is_python, etc. from free functions to properties of
Target
* Reduce the number of imports in __init__ files

Auditors: benjy

Conflicts:
	src/python/twitter/pants/tasks/task.py

(sapling split of 677780ea56af610359b3ccb30accb5b9ecd713d8)
pombredanne/pex,sixninetynine/pex,jamesbroadhead/pex,jamesbroadhead/pex,rouge8/pex,URXtech/pex,mzdanieltest/pex,pantsbuild/pex,kwlzn/pex,pombredanne/pex,kwlzn/pex,jsirois/pex,snyaggarwal/pex,sixninetynine/pex,snyaggarwal/pex,rouge8/pex,pantsbuild/pex,mzdanieltest/pex,URXtech/pex,jsirois/pex