Aded function from qiime.util inline

A function I was using (is_gzip) is not present in the version of QIIME
on the live system.  I copied-and-pasted the function the function inline
in run_process_sff_through_splib_lib.py so we can use it.
Added a note explaining the function's presence
Merge pull request #122 from adamrp/run_process_sff_through_split_libraries

stopgap fix for run_process_sff_through_split_lib.py