Merge branch 'master' into astropy

Merges up through r2072

Fixes #256, #309

Conflicts:

	astropy/io/fits/hdu/compressed.py
	astropy/io/fits/tests/test_core.py
	astropy/io/fits/tests/test_diff.py
	astropy/io/fits/tests/test_image.py
	astropy/io/fits/tests/test_table.py
	astropy/io/fits/util.py