Fix issue #1975, "svn switch does not update keywords".

* subversion/libsvn_wc/update_editor.c
  (update_keywords_after_switch_cb): New helper function
   which checks for the presence of an svn:keywords property
   and queues an install_file work queue item if present.
   Thus, when the work queue is run to complete the switch
   operation, all files with keywords will go through the
   translation process.
  (close_edit): If this is a switch operation, run a recursive
   proplist with the specified depth (infinity by default),
   invocing update_keywords_after_switch_cb() for each node
   with properties.

* subversion/tests/cmdline/switch_tests.py
  (switch_keywords, test_list): New test. Fails without
   the above change and passes with it.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1596591 13f79535-47bb-0310-9956-ffa450edef68