Support for synchronized native methods.

This change adds support for synchronized native methods by using
calls to MonitorEnter and MonitorExit on the JNIEnv*. There is
some tidying of the assembler and a straw man JNIEnv implementation.
The JNIEnv implementation just warns when MonitorEnter/Exit are called
and doesn't adhere to the correct JNIEnv layout.

Change-Id: I90ed6ec8f85f5b01b929f16e0dbdecadd0b01359
diff --git a/build/Android.common.mk b/build/Android.common.mk
index fe24801..24bfe02 100644
--- a/build/Android.common.mk
+++ b/build/Android.common.mk
@@ -38,6 +38,7 @@
 	src/dex_instruction.cc \
 	src/dex_verifier.cc \
 	src/jni_compiler.cc \
+	src/jni_internal.cc \
 	src/memory_region.cc \
 	src/object.cc \
 	src/raw_dex_file.cc \