krb5_try_realm_txt_rr() should allow the resolv library to expand

krb5_try_realm_txt_rr() should allow the resolv library to expand
the local domain or domain searchlist when the query is being
performed without the specification of a hostname or domain.
When 'name' is NULL or "", no '.' should be appended to the query.
Appending a '.' in that circumstance will result in an inability
to resolv the REALM if gethostname() does not return a fully
qualified domain name as on Windows and Solaris.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@11536 dc483132-0cff-0310-8789-dd5450dbe970