Fix documentation for ENV.each to return ENV

Also have spec check that it returns ENV.

Mostly from burdettelamar@yahoo.com (Burdette Lamar).

Fixes [Bug #16164]

hash.c

@@ -5276,9 +5276,9 @@ env_each_value(VALUE ehash)
 
 /*
  * call-seq:
- *   ENV.each      { |name, value| block } -> Hash
+ *   ENV.each      { |name, value| block } -> ENV
  *   ENV.each                              -> Enumerator
- *   ENV.each_pair { |name, value| block } -> Hash
+ *   ENV.each_pair { |name, value| block } -> ENV
  *   ENV.each_pair                         -> Enumerator
  *
  * Yields each environment variable +name+ and +value+.

spec/ruby/core/env/shared/each.rb

@@ -8,7 +8,7 @@
       ENV.clear
       ENV["foo"] = "bar"
       ENV["baz"] = "boo"
-      ENV.send(@method) { |k, v| e << [k, v] }
+      ENV.send(@method) { |k, v| e << [k, v] }.should equal(ENV)
       e.should include(["foo", "bar"])
       e.should include(["baz", "boo"])
     ensure