Fix typo in script data directory start_parallel_jobs_sge
Add system_call function

system_call() will be used in new all_tests.py script and
is based off of qiime_system_cal()
Add script level testing

In addition to module testing, all_tests.py will run each script and
check for proper completion. The script level testing is only done if
QIIME is installed (otherwise it is skipped without errors) since
it calls functionality from that package.

Fix #78.
Fix reference before assignment error when QIIME is not installed.
Update all_tests.py

Add myself to credits list and indicate that code is based off of QIIME's all_test.py code (instead of using previous biom-format code).
Update util.py

Add note indicating that system_call() came from QIIME's qiime_system_call()
Merge pull request #122 from mlangill/issue78

Add script level testing to all_tests.py