Follow up to r6066 with a clearer error message:
Follow up to r6066 with a clearer error message:

* subversion/libsvn_client/checkout.c
  (svn_client__checkout_internal): Don't speculate, just say what is known.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion