Tweak to option default extraction for help display.
Review Request #2640 — Created Aug. 16, 2015 and submitted
Previously a boolean option with no explicit default displayed as 'None' instead of 'False' or 'True' as appropriate. Added a bunch of tests for this, and also for flag scoping.
CI in flight: https://travis-ci.org/pantsbuild/pants/builds/75834137.
Revision 2 (+51 -12)