Revision 1854887

Merge the r1851676 group from trunk:

 * r1851676, r1851687, r1851791
   Allow the use of empty groups in authz rules.
   Justification:
     Fixes regression from 1.9.x. Does not affect authz file semantics.
   Notes:
     - r1851676 adds a regression test.
     - r1851687 fixes the bug and extends the test.
     - r1851791 refers to issue #4802.
   Votes:
     +1: brane, julianfoad, stsp