Ensure that we don't install Python 2.7.9 on Travis (use 2.7.8 instead) otherwise we get certificate erros due to the changes to certificate verification in 2.7.9 (see PEP 476).
Merge pull request #3202 from astrofrog/fix-conda

Disable conda update since latest version breaks SSL certificate checks
Add section on related Astropy packages to the docs
Copy photutils.utils functions
Update imports for new functions
Replace fix_prf_nan with mask_to_mirrored_num
Add tests for mask_to_mirrored_num
Add mask_to_mirrored_num to __all__
Update mask_to_mirrored_sum docs
Add example for mask_to_mirrored_num
Fix failure with Numpy 1.6. Fixes astropy/imageutils#22.
Refactored scale_img
Rename find_imgcuts in tests
Remove tests with min/max cuts
Rename scaling functions in tests
Fix scale_img docstring template
Update __all__
Rename scaling to scale
More docs for scale_img
Fix noise_level default