Minor fixes.

Quieted a couple of warnings about constness.

Added "synchronized" to BootClassLoader.getInstance(), which creates the
instance on first use.

Change-Id: I4a521bb2c6853b1ad8a118aa53f697be18b69280
diff --git a/vm/alloc/MarkSweep.c b/vm/alloc/MarkSweep.c
index 459a238..223448a 100644
--- a/vm/alloc/MarkSweep.c
+++ b/vm/alloc/MarkSweep.c
@@ -357,7 +357,7 @@
  */
 static void scanStaticFields(const ClassObject *clazz, GcMarkContext *ctx)
 {
-    StaticField *f;
+    const StaticField *f;
     int i;
 
     //TODO: Optimize this with a bit vector or something