BulletSim: add osGetPhysicsEngineType() LSL function and update

the physics engines to return the name that is specified in the INI
file ("physics = XXX") as the type of engine.
This os function is a little different than the others in that it
does not throw an exception of one is not privilaged to use it.
It merely returns an empty string.

OpenSim/Region/ScriptEngine/Shared/Api/Interface/IOSSL_Api.cs

@@ -259,6 +259,7 @@ namespace OpenSim.Region.ScriptEngine.Shared.Api.Interfaces
 
         string osGetScriptEngineName();
         string osGetSimulatorVersion();
+        string osGetPhysicsEngineType();
         Object osParseJSONNew(string JSON);
         Hashtable osParseJSON(string JSON);