On the log-message-templates branch, add an API to obtain log
message templates for a given set of working copy nodes instead
of a list of commit items obtained from the commit harvester.

This is useful for GUI clients which allow users to specify a
commit target list and log message in advance, i.e. before
svn_client_commit() and the commit harvester even get to run.

Suggested by: rhuijben

* subversion/include/svn_client.h
  (svn_client_get_log_message_templates): Declare.

* subversion/libsvn_client/commit_util.c
  (get_log_message_templates): Rename to ...
  (svn_client_get_log_message_templates): ... this, and change the
   input argument list of commit items to a list of absolute paths.
  (svn_client__get_log_msg): Create a list of abspaths from the commit
   items list so we can call svn_client_get_log_message_templates().


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/log-message-templates@1622692 13f79535-47bb-0310-9956-ffa450edef68