Delete CASGatewayCookie after successful authentication.  This allows
people to reauthenticate after their mod_auth_cas session times out.

- fixed indentation in mod_auth_cas.c
- added removeGatewayCookie_test to mod_auth_cas_test.c

removeGatewayCookie_test now calls cas_authenticate() and verifies result

fixed spacing, do not set request->user before cas_authenticate()