[PATCH 115/153] detect namespace packages from repository contents
[PATCH 115/153] detect namespace packages from repository contents

Instead of requiring all BUILDs to specify namespace packages, properly
define namespace packages in twitter/__init__.py,
twitter/common/__init__.py, etc.  This also slightly refactors how we do
package/resource detection so that it's a little more robust/testable.

RB_ID=223027

(sapling split of 0e6b2e5cfa02deafbb1ddd16e188e9e24f5f7b29)

(sapling split of 72190ec2c179e8a81b22fde8f899b2874dec66b4)
jamesbroadhead/pex,mzdanieltest/pex,pantsbuild/pex,kwlzn/pex,URXtech/pex,pombredanne/pex,rouge8/pex,snyaggarwal/pex,jsirois/pex,rouge8/pex,kwlzn/pex,pombredanne/pex,snyaggarwal/pex,mzdanieltest/pex,jamesbroadhead/pex,jsirois/pex,sixninetynine/pex,pantsbuild/pex,URXtech/pex,sixninetynine/pex