Fixes relating to 003-omnibus-opcodes

Fix computation of bits needed for a PC in GC map.
In the case that ClassLinker::FindClass fails with a class loader,
ignore the exception and raise a NoClassDefFoundError.
Elide callee-save methods from stack traces.

Change-Id: Ie0b7a544816e0c28d0f7df5821828aa84267cab7
diff --git a/src/thread.cc b/src/thread.cc
index 7e38290..f6ce34d 100644
--- a/src/thread.cc
+++ b/src/thread.cc
@@ -989,7 +989,9 @@
       skipping_ = false;
     }
     if (!skipping_) {
-      ++depth_;
+      if (frame.HasMethod()) {  // ignore callee save frames
+        ++depth_;
+      }
     } else {
       ++skip_depth_;
     }
@@ -1043,6 +1045,9 @@
       skip_depth_--;
       return;
     }
+    if (!frame.HasMethod()) {
+      return;  // ignore callee save frames
+    }
     method_trace_->Set(count_, frame.GetMethod());
     pc_trace_->Set(count_, pc);
     ++count_;