[krbdev.mit.edu #7688] Fix gss_krb5_set_allowable_enctypes for acceptor

[Greg Hudson via RT]

The test script won't backport directly because of the run_as_client -> 
run change in k5test.py in master.  It will probably work if we change 
"run" to "run_as_client" in the 1.11 backport of the script.  
Alternatively, we could omit the tests when backporting.