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
Change Table so assigning to non-existent col name creates new column with that value
Allow for multidimensional data when setting with t['new'] = newcol
Check that item is string when creating a new table column

Previous version broke setting rows with t[1] = (values) because
it tried to create a new column 1.  Instead make sure the item is
a string and is therefore referring to a column name.
Fix problem adding new column to an empty table
Add tests for creating a new column using item setter
Propagate Column metadata when creating column using item setter