Clarified distinction between running tests in source code vs. installed version

closes #795
adjusted wording on astropy.test() to "may not work"
change set width to maximum width
Added test to check download_file error type (issue pointed out by @kbarbary)
Fix attempt to access errno when the exception sometimes doesn't have it

Closes #808
created self.warnings outside except block
Fixes #725. Moved the cython_version.py generation until after the normal build_ext command runs.  There was really no specific reason for it to go first.  Also check to ensure that the build/lib directory exists yet before doing anything with it.
Add initial infrastructure for io.ascii meta handling
Update DAOphot reader to use new meta infrastructure
Parse IPAC table metadata (keywords and comments)
Fix mistake in IPAC reader docstring
Fix compatibility with Numpy 1.4.1
Improve DAOphot and IPAC reader docstrings
Improve the CDS reader doc string regarding metadata
Update IPAC docstring to fix an error in sphinx build
Change the default floating point output in VOTable from '%g' to '%s'.  This does a better job of showing "enough" precision to correctly roundtrip the values.
Make IPAC and DAOphot examples work literally and show output
When downloading a file, and we know it's size from the header, check that the temp filesystem and, if necessary, the cache filesystem have enough space before beginning the download.
Prevent downloading a file twice when identifying and reading it through the registry system.
Add TimePlotDate format for input to matplotlib plot_date()