Working fix for unsigned int conversions
Convert print statement to warning
All uint tests now working
missing colon
parametrize test and other minor changes
Also parametrize uint image tests
fully parametrize uint tests
Fix different hdu number in compressed files.  Also, closes #362 and closes #880
Disable test of 64-bit compressed image
add placeholder for uint parameter
Fix bad except statement
Fix test parameter
Restructure test parameters
Change the way column attributes are assigned
Add a system whereby collections of units can be enabled after the fact.
Add additional units in CDS/Vizier format
Move % and --- to the cds.py unit collection
Make Crab completely CDS-specific
Fixups after rebase
update nduncertainty for multiple/divide