Read multiaperture daophot file

I have added a few lines of code in get_cols() function of daophot.py to enable it to read daophot files which contain multiple aperture data.

daophot3.dat is a sample daophot file with multiple aperture data.
Also added a test_daophot_multiple_aperture() in tests/test_read.py  for test.

This is related to Issue #904
I think there should be a space after the comma and around the equal sign for readability such as `ap1, apN, apstep = (float(i) for i in aper.split(':'))` - see PEP 8
http://astropy.readthedocs.org/en/latest/development/codeguide.html#coding-style-conventions