[krbdev.mit.edu #4024] gss_acquire_cred auto prompt support shouldn't break gss_krb5_ccache_name()

[Alexandra Ellwood via RT]

gss_acquire_cred auto prompt support currently breaks gss_krb5_ccache_name().  If someone 
has set the ccache name and asks for a particular name, gss_acquire_cred does not look for the 
desired name in the ccache first but instead walks the cache collection looking for it.

I believe this is broken on both the KLL and the Leash versions of the code.

Noticed this because it break kadmin when you have tickets in your cache collection for the 
principal you are using with kadmin.