Testing the template_context_prerender hook

Testing the template_context_prerender hook

This allows for modifying any context *right before render*, including
access to the variables that are passed in.  This test takes advantage
of that and takes one of the variables, "doubleme", and modifies
it (doubles it!)

In our case it turns "happy" and "joy" into "happyhappy" and "joyjoy".

This commit sponsored by Mark Holmquist.  Thank you!