public class AllHttpScopesHashModel
An extension of SimpleHash that looks up keys in the hash, then in the
request, session, and servlet context scopes. Makes "Application", "Session"
and "Request" keys largely obsolete, however we keep them for backward
compatibility (also, "Request" is required for proper operation of JSP
It is on purpose that we didn't override keys and values
methods. That way, only those variables assigned into the hash directly by a
subclass of FreemarkerServlet that overrides
preTemplateProcess) are discovered as "page" variables by the FM
JSP PageContext implementation.