Change test for case sensitivity to succeed if default header is case sensitive
Change test for case sensitivity to succeed if default header is case sensitive

In essence, a check for astropy/ccdproc#156

evertrol/ccdproc,pulsestaysconstant/ccdproc,crawfordsm/ccdproc,mwcraig/ccdproc,astropy/ccdproc,indiajoe/ccdproc