Changes "is" and equality checks to strictly check for primitive types, fix a couple of

compiler/lib/implementation/number.dart

Index: compiler/lib/implementation/number.dart
===================================================================
--- compiler/lib/implementation/number.dart	(revision 400)
+++ compiler/lib/implementation/number.dart	(working copy)
@@ -55,8 +55,7 @@
     return truncated;
   }
 
-  NumberImplementation toDouble() { return this; }
-
+  NumberImplementation toDouble() native;
   String toString() native;
   String toStringAsFixed(int fractionDigits) native;
   String toStringAsExponential(int fractionDigits) native;
@@ -64,4 +63,5 @@
   String toRadixString(int radix) native;
 
   int hashCode() native;
+  get dynamic() { return toDouble(); }
 }