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.cc b/src/stack.cc
index 1e1f932..9589b57 100644
--- a/src/stack.cc
+++ b/src/stack.cc
@@ -45,11 +45,11 @@
   return *reinterpret_cast<uintptr_t*>(pc_addr);
 }
 
-uintptr_t Frame::GetVReg(Method* method, int vreg) const {
+uint32_t Frame::GetVReg(Method* method, int vreg) const {
   DCHECK(method == GetMethod());
   int offset = oatVRegOffsetFromMethod(method, vreg);
   byte* vreg_addr = reinterpret_cast<byte*>(sp_) + offset;
-  return *reinterpret_cast<uintptr_t*>(vreg_addr);
+  return *reinterpret_cast<uint32_t*>(vreg_addr);
 }
 
 uintptr_t Frame::LoadCalleeSave(int num) const {