[krbdev.mit.edu #8737] gss_add_cred() ignores desired_name if creating a new credential

[Greg Hudson via RT]

Side note: in the Solaris mechglue after the fix, if no desired_name is 
given but an input cred handle is given, the mechglue attempts to apply 
the name from the credential (remembered in the auxinfo structure, 
which we eliminated in commit 
889d3ca4c482f730cd194f2d83c41d70bc615a67).  Heimdal does not do this 
and I don't believe we need to either.