remove _null and _undefined

they have no significant effect on minified and gziped size. in fact
they make things worse.

file        | before     | after removal
----------------------------------------
concat      | 325415     | 325297
min         | 62070      | 62161
min + gzip  | 25187      | 25176

The bottom line is that we are getting 0.05% decrease in size after
gzip without all of the hassle of using underscores everywhere.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/apis.js b/src/apis.js
index 1ca33208..9311c620 100644
--- a/src/apis.js
+++ b/src/apis.js
@@ -1,6 +1,6 @@
 var angularGlobal = {
   'typeOf':function(obj){
-    if (obj === _null) return $null;
+    if (obj === null) return $null;
     var type = typeof obj;
     if (type == $object) {
       if (obj instanceof Array) return $array;