/**
* 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) {