Add timestamp checking to template compilation.

This is a fix for issue #74 which complains that changes to template files don't get recompiled when a page is rendered/refreshed.  I've only tested enough to see that the switch does indeed enable/disable timestamp checking (the default is enabled).

The patch includes a change in DefaultSessionStore needed for this code to compile for me.  I'm using Java 6 and it complains that Gauva's CacheBuilder.newBuilder method doesn't want a type filler.