Ev2 shims: Add a base fetching function for the svnrdump dump editor.
Ev2 shims: Add a base fetching function for the svnrdump dump editor.

Current number of Ev2 test failures: 258

* subversion/svnrdump/dump_editor.c
  (fetch_base_func): New.
  (svn_rdump__get_dump_editor): Use the base fetching function.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1229467 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion