Fixes a crash introduced in fd187f466f by ensuring that the CScriptValRooted values are destroyed before calling JS_DestroyContext.

I've tested the performance on Combat Demo (Huge) again with the code
from #2394.
It's very close but probably a little bit lower (hard to tell because
it's so close).

Closes #2408
Refs #2394

This was SVN commit r14705.

source/scriptinterface/ScriptInterface.h

@@ -91,8 +91,6 @@ public:
 	 */
 	static shared_ptr<ScriptRuntime> CreateRuntime(int runtimeSize = DEFAULT_RUNTIME_SIZE);
 
-	CScriptValRooted vector2Dprototype;
-	CScriptValRooted vector3Dprototype;
 
 	/**
 	 * Constructor.
@@ -130,6 +128,9 @@ public:
 	 */
 	bool LoadGlobalScripts();
 
+	enum CACHED_VAL { CACHE_VECTOR2DPROTO, CACHE_VECTOR3DPROTO };
+	CScriptValRooted GetCachedValue(CACHED_VAL valueIdentifier);
+
 	/**
 	 * Replace the default JS random number geenrator with a seeded, network-sync'd one.
 	 */