Fix Mac OS X build since we upgraded to go1.2.

Since go1.2, the release engineers have keyed their release
artifacts to the major release family of Mac OS X.

Change-Id: Ia4bf0c86af9884748e21be14ab6e09f01a830e19

Makefile.INCLUDE

@@ -28,12 +28,23 @@ endif
 OS=$(shell uname)
 ARCH=$(shell uname -m)
 
+# The release engineers apparently need to key their binary artifacts to the
+# Mac OS X release family.
+MAC_OS_X_VERSION ?= 10.8
+
 BUILD_PATH = $(PWD)/.build
 
-GO_VERSION	 := 1.2
+GO_VERSION	 := 1.2.1
 GOOS		  = $(subst Darwin,darwin,$(subst Linux,linux,$(OS)))
+
+ifeq ($(GOOS),darwin)
+RELEASE_SUFFIX ?= -osx$(MAC_OS_X_VERSION)
+else
+RELEASE_SUFFIX ?=
+endif
+
 GOARCH		  = $(subst x86_64,amd64,$(ARCH))
-GOPKG		 ?= go$(GO_VERSION).$(GOOS)-$(GOARCH).tar.gz
+GOPKG		 ?= go$(GO_VERSION).$(GOOS)-$(GOARCH)$(RELEASE_SUFFIX).tar.gz
 GOURL		 ?= http://go.googlecode.com/files
 GOROOT		  = $(BUILD_PATH)/root/go
 GOPATH		  = $(BUILD_PATH)/root/gopath