Removed the --use_sfftools flag from the call to process_sff.py
Undid previous commit, added logic for file naming

The only time --use_sfftools was passed to process_sff was
for the list of special cases in
run_process_sff_through_split_lib.py, and it is needed there
to use --notrim. The upshot is gzipped SFFs now work in all
cases UNLESS that SFF is in the special cases list.
Added code to test file extension as well as type

is_gzip tests the file type, but there is a small chance that the
file might be a gzip and not end in '.gz'. This rare case should no
longer be a problem.
Added a gzipepd SFF to support files, added test code
Merge pull request #120 from adamrp/gzipped_sffs

gzipped SFF files will now work