Bump 1.6.x branch to 1.6.22.

* STATUS,
  subversion/include/svn_version.h: Update to 1.6.22



git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.6.x@1462381 13f79535-47bb-0310-9956-ffa450edef68