cacheToFile (SQLRCursor)

    /**
     *  call-seq:
     *  cacheToFile(filename)
     *
     *  Sets query caching on.  Future queries will be cached to the
     *  file "filename".
     *
     *  A default time-to-live of 10 minutes is also set.
     *
     *  Note that once cacheToFile() is called, the result sets of all
     *  future queries will be cached to that file until another call to
     *  cacheToFile() changes which file to cache to or a call to
     *  cacheOff() turns off caching. */
    static VALUE sqlrcur_cacheToFile(VALUE self, VALUE filename) {