/**
 *  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) {