Use the DEFAULT_COMPRESSION_TYPE constant here instead of hard-coding RICE_1

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2267 ed100bfc-0583-0410-97f2-c26b58777a21
Adds full support for the ZQUANTIZ and ZDITHER0 keywords.  This fixes spacetelescope/PyFITS#32 and makes the sample image from the user's original bug report readable.  It also makes it possible to write new images using one of the two dithering methods supported by CFITSIO.

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2268 ed100bfc-0583-0410-97f2-c26b58777a21