Fix makefile for building non-head packages.

Because we use an index checkout to replace the composer provided
package we should ensure to checkout the specific version. This helps to
ensure that old packages are built correctly.

The APP_VERSION variable is required when building packages for 3.1 and
3.0 releases. The current app version requires several packages that
rely on 3.2 things.

Refs #8585

Makefile

@@ -23,6 +23,13 @@ endif
 
 DASH_VERSION=$(shell echo $(VERSION) | sed -e s/\\./-/g)
 
+# Used when building packages for older 3.x packages.
+# The build scripts clone cakephp/app, and this var selects the
+# correct tag in that repo.
+# For 3.1.x use 3.1.2
+# For 3.0.x use 3.0.5
+APP_VERSION:=master
+
 ALL: help
 .PHONY: help install test need-version bump-version tag-version
 
@@ -104,9 +111,12 @@ build:
 
 build/app: build
 	git clone git@github.com:$(OWNER)/app.git build/app/
+	cd build/app && git checkout $(APP_VERSION)
 
 build/cakephp: build
+	git checkout $(VERSION)
 	git checkout-index -a -f --prefix=build/cakephp/
+	git checkout -
 
 dist/cakephp-$(DASH_VERSION).zip: build/app build/cakephp composer.phar
 	mkdir -p dist