Various things.

This patch:

1. adds good-enough implementations for a couple of Class native methods we
need.

2. removes a fixed TODO from image_test.

3. adds missing null checks to the Thread native methods, and forwards
Thread.nativeCreate to Thread::Create.

4. stops jni_compiler from overwriting already-registered native methods
with the dynamic lookup stub.

5. adds workarounds to Thread::CreatePeer so we can cope better without
code, attempts to initialize thread groups correctly, dumps thread state
from the managed peer (where one exists), and implements Thread::DumpStack
for debugging (and SIGQUIT dumps).

Change-Id: I3281226dd22ec852dca5165748fc75a254904ac0
diff --git a/src/image_test.cc b/src/image_test.cc
index 0bd79db..02a7d69 100644
--- a/src/image_test.cc
+++ b/src/image_test.cc
@@ -71,8 +71,7 @@
   ASSERT_TRUE(boot_space != NULL);
 
   // enable to display maps to debug boot_base and boot_limit checking problems below
-  // TODO: why does this dump show two attached threads?
-  if (true) {
+  if (false) {
     SignalCatcher::HandleSigQuit();
   }