Enable single-DB mode.
Enable single-DB mode.

* subversion/libsvn_wc/wc.h
  (SVN_WC__SINGLE_DB, SINGLE_DB): Define if SVN_WC__VERSION >= 19.  Move to
    after the definition of SVN_WC__VERSION.
  (SVN_WC__VERSION): Bump to 19 and document the change.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@991236 13f79535-47bb-0310-9956-ffa450edef68

wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion