Merge pull request #11 from josePhoenix/master

Improve robustness of setup.py in the absence of certain dependencies
Bug fix to compound optics; fixes issue #6. Also adds unit test.
test_matrixDFT should not try to write test output FITS files by default.
Rework FFT config to combine checks for use_fftw and presence of fftw
Following discussion & suggestions on https://github.com/astropy/package-template/issues/106
Merge branch 'master' into zernike

Conflicts:
	poppy/optics.py