Fixes a problem with the ls command and specifying a revision keyword with
a working copy path.

* subversion/libsvn_client/ls.c
  (svn_client_ls): Pass the working copy path to get the revision number, or
  NULL if the path is a URL.

* subversion/tests/clients/cmdline/basic_tests.py
  (basic_ls): Updated to include a test using the BASE revision keyword.