Upgrade twitter/commons to pants 0.0.26.

Fixup BUILDs, plugins and scripts to work with pants API changes.

Run the migrate_config tool from pants to convert many pants.ini sections
and keys.  Also kill some un-needed keys.

Prepare a twitter.common.pants 0.7.0 release.

Upgrade BUILD.tools and fix code to conform to more stringent checkstyle
and jmake expectations that result.

Also upgrade to virtualenv 1.11.6 and allow custom PIP_OPTIONS to
be specified (useful for bootstrapping pants as eggs in the venv for
easy IDEA project setup to hack on ants-plugins).