Refactored common test code.
Refactored common test code.

Finished refactoring comparisons for splines

Changed `assert_equal` to `assert_allclose` in all tests.


saimn/astropy,pllim/astropy,saimn/astropy,saimn/astropy,lpsinger/astropy,larrybradley/astropy,mhvk/astropy,pllim/astropy,astropy/astropy,lpsinger/astropy,StuartLittlefair/astropy,StuartLittlefair/astropy,saimn/astropy,mhvk/astropy,astropy/astropy,StuartLittlefair/astropy,larrybradley/astropy,lpsinger/astropy,mhvk/astropy,mhvk/astropy,astropy/astropy,larrybradley/astropy,mhvk/astropy,pllim/astropy,StuartLittlefair/astropy,lpsinger/astropy,astropy/astropy,lpsinger/astropy,larrybradley/astropy,StuartLittlefair/astropy,astropy/astropy,saimn/astropy,larrybradley/astropy,pllim/astropy,pllim/astropy