Fix generic warning class for inverted locations in BioSQL
Fix generic warning classes in BioSQL/Loader.py
Fix generic warning class for BioSQL PostgreSQL schema rules
Hide scary but harmless warnings in BioSQL tests
run_tests.py doesn't see these MissingExternalDependencyError exceptions so not skipped

The MissingExternalDependencyError should be raised at import time
in order that run_tests.py can skip the unit test. Removing the
try/except as it was hiding the underlying network error, e.g.
HTTPError: HTTP Error 502: Bad Gateway

We might want to add a quick check to see if the NCBI Entrez site
is live at the start of test_SeqIO_online.py instead...
Be consistent about Entrez.email used in unittests
Another generic warning changed to a BiopythonWarning
Make this generic warning into a BiopythonWarning
Check BiopythonWarning messages in test_SeqIO.py

Partly due to previous commit to the Bio/SeqIO/InsdcIO.py annotation
'too long' warning where I switched it from a generic UserWarning
to a BiopythonWarning, but also a good idea in general I hope.