Make some 'svn mkdir' code use absolute paths internally, to avoid path length
limits on Windows.

* subversion/libsvn_client/add.c
  (svn_client__make_local_parents): Document as taking absolute paths, and
    don't hide errors.
  (svn_client_mkdir4): Make dirents absolute before passing them to
    svn_client__make_local_parents.

* subversion/libsvn_client/client.h
  (svn_client__make_local_parents): Tweak prototype.

Found by: schabi


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1516816 13f79535-47bb-0310-9956-ffa450edef68