Uncomment objc tests

BUILD

@@ -124,13 +124,13 @@ cc_library(
     deps = [":protobuf_lite"],
 )
 
-# objc_library(
-#     name = "protobuf_objc",
-#     hdrs = ["objectivec/GPBProtocolBuffers.h"],
-#     includes = ["objectivec"],
-#     non_arc_srcs = ["objectivec/GPBProtocolBuffers.m"],
-#     visibility = ["//visibility:public"],
-# )
+objc_library(
+    name = "protobuf_objc",
+    hdrs = ["objectivec/GPBProtocolBuffers.h"],
+    includes = ["objectivec"],
+    non_arc_srcs = ["objectivec/GPBProtocolBuffers.m"],
+    visibility = ["//visibility:public"],
+)
 
 RELATIVE_WELL_KNOWN_PROTOS = [
     # AUTOGEN(well_known_protos)
@@ -470,6 +470,8 @@ java_library(
 # Python support
 ################################################################################
 
+# Requires: six for python 2/3 compatibility.  `pip install six`
+
 # Hack:
 # protoc generated files contain imports like:
 #   "from google.protobuf.xxx import yyy"