Checkpoint a new libsvn_client api that when tested can replace most of the
svnmucc code, while re-using some of the commit infrastructure in
libsvn_client.

Most of the code is implemented now, so in theory it should work, but to
prove or disprove that the next step will be writing some testcases :)

* subversion/include/svn_client.h
  (svn_client_mtcc_t): New typedef.
  (svn_client_mtcc_create
   svn_client_mtcc_get_relpath
   svn_client_mtcc_add_add_file
   svn_client_mtcc_add_copy
   svn_client_mtcc_add_delete
   svn_client_mtcc_add_mkdir
   svn_client_mtcc_add_move
   svn_client_mtcc_add_propset
   svn_client_mtcc_add_update_file
   svn_client_mtcc_commit): New functions.

* subversion/libsvn_client/mtcc.c
  New file.

* subversion/libsvn_client/mtcc.h
  New file.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1550758 13f79535-47bb-0310-9956-ffa450edef68