Remove code duplication.

* subversion/libsvn_ra_svn/client.c
  (ra_svn_open): Switch to dual-pool and ...
  (ra_svn_open_pool): ... add a single-pool wrapper.
  (ra_svn_dup_session): Call ra_svn_open instead of duplicating code.
  (ra_svn_vtable): Use single-pool wrapper.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1607212 13f79535-47bb-0310-9956-ffa450edef68