Bug 807151 - Unexport |mozilla| from the |js| namespace; r=Waldo

Clang does not want to allow js::ion::Range and mozilla::Range simultaneously
when we have a |namespace js { using namespace mozilla; }| declaration.

js/src/jsdate.cpp

@@ -50,10 +50,11 @@
 
 #include "vm/Stack-inl.h"
 
-using namespace mozilla;
 using namespace js;
 using namespace js::types;
 
+using mozilla::ArrayLength;
+
 /*
  * The JS 'Date' object is patterned after the Java 'Date' object.
  * Here is an script: