* subversion/libsvn_wc/adm_ops.c   (svn_wc__set_file_external_location): Turn a user triggerable assertion      into a proper error.
* subversion/libsvn_wc/adm_ops.c
  (svn_wc__set_file_external_location): Turn a user triggerable assertion
     into a proper error.

Found by: danielsh

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