Add wcscheck utility

Add documentation for wcslint
Fix for Python 2.6, which is missing PyErr_NewExceptionWithDoc
Fix Python 3 issues
Allow affiliated packages to generate their own cython_version.py module.
Some superfluous whitespace fixes
Adds a test and kind of hacky fix for #1244. Basically we try to decode the byte string using locale.getpreferredencoding(), but if that returns an invalid encoding we try decoding with utf-8. If that fails (do to undecodable bytes) we just fall back on latin-1.  Therefore we always output *something* though there's no 100% guarantee it won't be gibberish if the system's default encoding is incorrect.
Per the comment in this commit, distribute_setup.py assumes that if you had to download distribute you did *not* already have the pkg_resources, which is a false assumption on Ubuntu. Make sure to pkg_resources is unloaded before importing the newly downloaded setuptools, because we want to use the pkg_resources that it ships with and not the one installed by the system.
Document the new `tests.helper.catch_warnings` context manager.
Use `tests.helpers.catch_warnings` instead of `warnings.catch_warnings`
Merge pull request #1244 from iguananaut/issue-1244

Problems with logging in some systems
Merge pull request #1265 from mdboom/testing/use-catch-warnings

Use astropy.tests.helpers.catch_warnings instead of warnings.catch_warnings
Use .utils._compiler instead of astropy.utils._compiler to force affilated packages to report the compiler they were built with, not the compiler Astropy was built with.  This will require an update the package-template to include support for this optional feature.  The instructions for setting up the package should include removing this if the package does not include any compiled C extensions (in which case it's superfluous).
PEP8 spacing fix
Allow non-strings to be logged without raising a TypeError
Merge pull request #1267 from barentsen/allow-logging-non-strings

Allow non-strings to be logged without raising a TypeError
Merge pull request #580 from mdboom/wcs/lint

Consider having a wcscheck utility
Add the release date of 0.2.3 and add a placeholder for 0.2.4.
Merge pull request #1198 from iguananaut/issue-1198

Make ``cython_version`` logic affiliated package-friendly
Add a troubleshooting tip about the Windows registry.  This is basically the same text I added to the PyFITS FAQ but s/PyFITS/Astropy
Merge pull request #1151 from iguananaut/issue-1151

Distribution instance has no attribute 'exclude_package_data'