Fix issue 3437, rep-cache.db created with wrong permissions.

* subversion/libsvn_fs_fs/rep-cache.c
  (open_rep_cache): Create file before calling into SQLite.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1547866 13f79535-47bb-0310-9956-ffa450edef68