Implement getting of 64-bit locals (double, long).

Also implement the JDWP "GetClassLoader" request, used by jswat's "classes"
command.

Also implement the JDWP "exit" request, tested with jswat's "shutdown".

Change-Id: Ic8424a332151242211d8a772721deb3199b24682
diff --git a/src/stack.h b/src/stack.h
index f1fb08f..680a69d 100644
--- a/src/stack.h
+++ b/src/stack.h
@@ -54,7 +54,7 @@
 
   uintptr_t LoadCalleeSave(int num) const;
 
-  uintptr_t GetVReg(Method* method, int vreg) const;
+  uint32_t GetVReg(Method* method, int vreg) const;
 
   Method** GetSP() const {
     return sp_;