Add security_token parameter to STSConnection
Fix #1898 by doing an initial call to `datetime.strptime`

This commit works around an upstream threading bug
http://bugs.python.org/issue7980 which affects Mac OS X. It includes a
test which is skipped by default because it will not always fail.
Merge pull request #1940 from danielgtaylor/strptime-bug

Fix #1898, #1940 by doing an initial call to `datetime.strptime`
Updated all old-style inheritance calls.
Add unit test for STS security_token
Merge pull request #1948 from danielgtaylor/jimbrowne-sts-secure-token

Pass security token through to STS connection. Fixes #1948, #1931.
Missed two spots for use of ``super(…)``.
Merge branch 'switch-to-super' into develop
Fixes #1918, #1936 & #1937.