Add table of built-in cosmologies, other minor documentation cleanups.

* closes #1147
Fix sphinx warning, add note about doc update

* Extra space before code block in Built-in Cosmologies section
  of index.rst
* Add warning to parameters.py to update the documentation table
  when adding a new cosmology
Put the astropy.wcs include headers under its own directory so they
aren't confused with other headers at the top-level (notably sip.h from PyQt).
Merge pull request #1528 from mdboom/wcs/include-in-subdirectory

unknown type name 'sip_t' [Xcode 5]
removed use of removed make_kernel from test_convolve_speeds.py

pointed out by @cdeil in #1509
Allow tuples to be passed to is_equivalent
Added note to changelog
Added a few negative assertions to test
Mention in API changes that the make_kernel function has been removed. Closes #1509.
Fix decoding of platform name.
Fix py.test 2.4.0 on Python 3.1
Don't need to use an explicit list
Merge pull request #1530 from mdboom/tests/encoding-is-none

py.test cannot run if sys.stdout.encoding is None
Merge pull request #1531 from mdboom/tests/fix-pytest-on-py3.1

Restore compatibility with Python 3.1?
Make sure the list of modules being iterated over cannot change during the iteration.
Merge pull request #1527 from aconley/cosmo_builtin_docs

Add table of built-in cosmologies, other minor documentation cleanups.
Merge pull request #1533 from astrofrog/fix-catch-warning-issue

Make sure the list of modules being iterated over cannot change during iteration
Change interpretation of lists in Table.__getitem__ (closes #274)
Duck type when item in __getitem__ is not one of a few specified possibilities
Add tests and documentation for getting sub-set of columns with list of names