Add the signal catcher (for SIGQUIT and SIGUSR1).

Also fix some of the thread implementation.

Change-Id: If2d1b59a149ba1ac192ad9bc74319c8dff228549
diff --git a/src/class_linker.h b/src/class_linker.h
index cb21cb1..c848825 100644
--- a/src/class_linker.h
+++ b/src/class_linker.h
@@ -38,6 +38,8 @@
     return FindClass(descriptor, NULL);
   }
 
+  size_t NumLoadedClasses() const;
+
   // Resolve a String with the given ID from the DexFile, storing the
   // result in the DexCache.
   String* ResolveString(const DexFile& dex_file,