Include held locks in SIGQUIT thread dumps.

Handy if you have an ANR that's locking related. Quick tour:

   at org.apache.harmony.dalvik.NativeTestTarget.emptyJniStaticSynchronizedMethod0(Native method)
   - locked <0x60135aa8> (a java.lang.Class<org.apache.harmony.dalvik.NativeTestTarget>)
   at java.lang.reflect.Method.invoke(Native method)
   at C.whileTrue(Main.java:63)
   at C.synchronizedOnClassString(Main.java:56)
   - locked <0x60002a70> (a java.lang.Class<java.lang.String>)
   at C.nestedSynchronizationWithTryCatch(Main.java:44)
   - locked <0x61336b90> (a java.lang.String)
   - locked <0x61336bd0> (a java.lang.String)
   at C.nestedSynchronization(Main.java:35)
   - locked <0x61336b18> (a java.lang.String)
   - locked <0x61336b50> (a java.lang.String)
   at C.synchronizedOnClassC(Main.java:30)
   - locked <0x613366f8> (a java.lang.Class<C>)
   at C.noLocks(Main.java:27)
   at C.<clinit>(Main.java:24)
   - locked <0x613366f8> (a java.lang.Class<C>)
   at Main.main(Main.java:19)

A non-static synchronized native method works too:

   at org.apache.harmony.dalvik.NativeTestTarget.emptyJniSynchronizedMethod0(Native method)
   - locked <0x613371a8> (a org.apache.harmony.dalvik.NativeTestTarget)
   ...

Note that most stack traces don't look any different; the above is a
pathological example that exercises different kinds of locking. Testing
with system_server shows most threads don't hold any locks.

Future work (marked by TODO) is that explicit JNI MonitorEnter calls in
native code aren't shown.

Change-Id: I2747f5cddb4ef64b1935736f084a68fe8e4005e9