Improve error messages on propset and propedit when an svn: property
is misspelled.

* subversion/svn/cl.h (svn_cl__prop_use_t): New enumeration.
  (svn_cl__check_svn_prop_name): Add prop_use parameter.
* subversion/svn/props.c (force_prop_option_message, wrong_prop_error_message):
   Two new helper functions that return a customized error message based
   on svn_cl__prop_use_t property use discriminator.
  (svn_cl__check_svn_prop_name): Update prototype with prop_use.
   Call the helpers to generate customized error messages based on the
   given property use.

* subversion/svn/propset-cmd.c (svn_cl__propset): Set property usage.
* subversion/svn/propedit-cmd.c (svn_cl__propedit): Set property usage.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1470781 13f79535-47bb-0310-9956-ffa450edef68