Read thread priority as an int, not a boolean.

We were using the wrong field get function.  After our change to
stdbool.h, the thread priority was always 0 or 1.
diff --git a/vm/Thread.c b/vm/Thread.c
index db64256..30c3523 100644
--- a/vm/Thread.c
+++ b/vm/Thread.c
@@ -1569,7 +1569,7 @@
      * setPriority(), and then starts the thread.  We could manage this with
      * a "needs priority update" flag to avoid the redundant call.
      */
-    int priority = dvmGetFieldBoolean(self->threadObj,
+    int priority = dvmGetFieldInt(self->threadObj,
                         gDvm.offJavaLangThread_priority);
     dvmChangeThreadPriority(self, priority);