Some slight tweaks to CompositeModels for the v0.3.2 release.  This doesn't add much improvement or fix any issues--instead it addresses issues like #1836 by being clearer about what these classes don't currently support.  It also slightly improves their text representations.
Added link to fperez's git notebook
Turn off parallel testing on Python 3.2, where it is still occasionally
flaky.  See https://travis-ci.org/astropy/astropy/jobs/24452287
Merge pull request #2438 from mdboom/test/turn-off-parallel-32

Turn off parallel testing on Python 3.2, where it is still occasionally flaky
Merge pull request #2432 from eteq/add-git-notebook

Added link to fperez's git notebook
Merge pull request #1836 from embray/issue-1836

param_sets method not working with SerialCompositeModel
Change allocation in WCS.sub.

Conflicts:
	astropy/wcs/src/wcslib_wrap.c
Add a comparison function for Wcsprm objects.
Simplify, based on Mark Calabretta's suggestion.
Updates after Mark Calabretta's feedback.
Remove excess parameters in call.