CustomKernel fixes
Added CustomKernel tests for zero-summed kernels.
Ignore differences between 32-bit and 64-bit ints
Fix equality for array coordinates

Closes #1832
Added test for #1832 failure mode
Add test for #2037 failure mode
update changelog
Get `Longitude` sign to come out right from `wrap_angle` when 0

Closes #2037
Fix test that incorrectly had '-0h00m00s 0d00m00s' and similar
Ignore long int suffix in doctests, e.g. 1234L
renamed deriv method to fit_deriv
rename 'deriv' to 'fit_deriv' in documenation
Clean up `setup.py test --help`
added an entry in the changelog
Make UTC the default time scale
Update tests for UTC default
Update docs for UTC default
Update CHANGES for UTC default
Fix spacing error
Fix rounding errors with fractional powers.