Added pre- hook to CRM_Core_BAO_CustomGroup::create().
CRM-14990: Don't force a value for is_reserved if it isn't passed into CRM_Core_BAO_CustomGroup::create().
CRM-14990. Update strictness of param comparison for consistency with the rest of Civi's codebase, per Eileen's recommendation: https://github.com/civicrm/civicrm-core/commit/f329e1deb8ebc36b68b3fe4448b16fc6f5cf52bd#commitcomment-7036984.
Merge pull request #3687 from GinkgoFJG/CRM-14990-2

CRM-14990: Round two.