1) With SETGID_MAIL enabled (only with dot locking), if the chgrp of

   inc fails during install, don't attempt to chmod it.  This will
   cause make install to fail, which is good in this case.
2) Added SETGID_MAIL= to the install by the test suite so that it
   does not attempt the chgrp+chmod.  The test suite didn't need them.
3) Removed the SETGID_MAIL= from the test suite invocation in build_nmh.
(cherry picked from commit 721276218bc03d4b0d86306c9b2990fae6f07426)