Merge pull request #1785 from mdboom/fix_bbox_test

Fix test_bbox_inches_tight
First pass at making setup more sane.
Removing dateutils, pytz and six (external Python dependencies)
Fix a few bugs in the build.
More fixes
setupegg.py is now redundant.
Fix type in dates docs
Update INSTALL document to reflect new reality
Handle dateutil and pyparsing in the same manner as everything else.
Raise exception early if pyparsing and/or dateutil are not installed.
Fix pyparsing on python 3 check
Fix build on Python 2.6
Update Travis dependencies
Implement a better way to handle overflow in the Agg backend.
Fix agg overflow test
Make using an external PyCXX possible on != Python 2.7
Fix infinite process recursion on Windows
Update to PyCXX 6.2.4
Update the CXX detection code to use the system PyCXX in more cases
Fix compiler warnings about compare_handler