fluxcal() minor change

- the PyRAF task sensfunc (and calibrate) requires you to input the root
name for your output sensitivity function file. Thus, the string
variable sensfile contained for example 'sens13.24flx001' instead of
'sens13.24flx001.fits' but pyfits.open() needs to be given the extension
(.fits) of the file as well. Thus, pyfits.open() is now fed
sensfile+'.fits' and same for the values in the dictionary sensfiles.
- Fixed a minor spelling error for the dictionary standardimages()
instead of stsandardimages() in indivtasks() option #20.