Started some refactoring on the compressed HDU module.  For a while now it hasn't been necessary to define a define a dummy class when the compression module is missing (and that didn't really work well anyways).  Now, if the compression module is missing, CompImageHDU.match_header() will just pass, and a BinTableHDU will be created instead.  Also added a couple lines to the constructor to make sure CompImageHDUs can't be manually created if the compression module is missing.
Started some refactoring on the compressed HDU module.  For a while now it hasn't been necessary to define a define a dummy class when the compression module is missing (and that didn't really work well anyways).  Now, if the compression module is missing, CompImageHDU.match_header() will just pass, and a BinTableHDU will be created instead.  Also added a couple lines to the constructor to make sure CompImageHDUs can't be manually created if the compression module is missing.

git-svn-id: 5305e2c1a78737cf7dd5f8f44e9bbbd00348fde7@986 ed100bfc-0583-0410-97f2-c26b58777a21

spacetelescope/PyFITS,embray/PyFITS,spacetelescope/PyFITS,embray/PyFITS,embray/PyFITS,embray/PyFITS