Release v3.19.1 - Bugfix: default GSSAPIDelegateCredentials to undef

This was previously set to undef everywhere except Solaris 11 which was
set incorrectly to 'yes'.
Merge pull request #89 from ghoneycutt/release_v3.19.1_bugfix_for_GSSAPIDelegateCredentials

Release v3.19.1 - Bugfix: default GSSAPIDelegateCredentials to undef