Pass entire Hdf to Extension::moduleLoad()

This lets us move parsing of runtime options
to the extensions which actually use them.

Nobody is currently using this functionality, so changing
what gets passed isn't a BC break worth worrying about.

I'll post some followup diffs pulling things out of
RuntimeOptions.

hphp/runtime/ext/extension.cpp

@@ -52,7 +52,7 @@ void Extension::LoadModules(Hdf hdf) {
   assert(s_registered_extensions);
   for (ExtensionMap::const_iterator iter = s_registered_extensions->begin();
        iter != s_registered_extensions->end(); ++iter) {
-    iter->second->moduleLoad(hdf["Extensions"][iter->second->m_name.c_str()]);
+    iter->second->moduleLoad(hdf);
   }
 }