Put verify option to ImageFileCollection?

[ysBach]

If a FITS file contains non-standard FITS header, the ImageFileCollection does not work:

from astropy.io import fits
import astropy
import ccdproc
import numpy as np

print(np.__version__)
# 1.13.3
print(astropy.__version__)
# 2.0.3
print(ccdproc.__version__)
# 1.3.0

'''
The test header looks like this:

NAXIS1  =                   10 / length of data axis 1                          
NAXIS2  =                   10 / length of data axis 2                          
TESTVERI= '2017/02/13-16:51:38 / Test VerifyWarning
'''

testh = fits.Header.fromtextfile('test_hdr.txt')
testfits = fits.PrimaryHDU(data=np.ones((10,10)), header=testh)
testfits.writeto('test_warnA.fits', output_verify='warn', overwrite=True)
ccdproc.ImageFileCollection('.', glob_include='*warnA*')

Traceback (most recent call last):

  File "<ipython-input-19-0eff28aafa40>", line 12, in <module>
    ccdproc.ImageFileCollection('.', glob_include='*warnA*')

  File "/home/aaa/anaconda3/lib/python3.6/site-packages/ccdproc/image_collection.py", line 153, in __init__
    self.keywords = keywords

  File "/home/aaa/anaconda3/lib/python3.6/site-packages/ccdproc/image_collection.py", line 302, in keywords
    self._summary = self._fits_summary(new_keys_lst)

  File "/home/aaa/anaconda3/lib/python3.6/site-packages/ccdproc/image_collection.py", line 619, in _fits_summary
    missing_marker=missing_marker)

  File "/home/aaa/anaconda3/lib/python3.6/site-packages/ccdproc/image_collection.py", line 530, in _dict_from_fits_header
    for k, v in six.iteritems(h):

  File "/home/aaa/anaconda3/lib/python3.6/site-packages/astropy/io/fits/header.py", line 940, in iteritems
    yield (card.keyword, card.value)

  File "/home/aaa/anaconda3/lib/python3.6/site-packages/astropy/io/fits/card.py", line 285, in value
    self._value = self._parse_value()

  File "/home/aaa/anaconda3/lib/python3.6/site-packages/astropy/io/fits/card.py", line 744, in _parse_value
    ".verify('fix').".format(self.keyword))

VerifyError: Unparsable card (TESTVERI), fix it first with .verify('fix').

Maybe one possibility is to introduce a parameter like verify or verify_option which will be used to circumvent the default verify option "exception"?

[crawfordsm]

This seems like a reasonable request. If you have time to put in a pull request to address it, it would be very welcome!