Add a post-install script that points the link to the correct revision

rakefile

 require 'rake/clean'
 require 'tempfile'
 
+# Build Constants
 REPO_ROOT = File.dirname(__FILE__)
 BUILD_DIR = File.join(REPO_ROOT, "build")
+
+# Packaging constants
+DEPLOY_DIR = "/opt/wwc"
+PACKAGE_NAME = "mitx"
+LINK_PATH = File.join(DEPLOY_DIR, PACKAGE_NAME)
+VERSION = "0.1"
+
+# Set up the clean and clobber tasks
 CLOBBER.include('build')
-CLEAN.include("#{BUILD_DIR}/*.deb")
+CLEAN.include("#{BUILD_DIR}/*.deb", "#{BUILD_DIR}/util")
 
 task :package do
     commit = (ENV["GIT_COMMIT"] || `git rev-parse HEAD`).chomp()
@@ -13,20 +22,37 @@ task :package do
     build_number = (ENV["BUILD_NUMBER"] || "dev").chomp()
 
     if branch == "master"
-        package_name = "mitx"
+        deploy_name = "#{PACKAGE_NAME}-#{commit}"
     else
-        package_name = "mitx-#{branch}"
+        deploy_name = "#{PACKAGE_NAME}-#{branch}-#{commit}"
     end
+    INSTALL_DIR_PATH = File.join(DEPLOY_DIR, deploy_name)
 
     FileUtils.mkdir_p(BUILD_DIR)
     
     Dir.chdir(BUILD_DIR) do
+
+        postinstall = Tempfile.new('postinstall')
+        postinstall.write <<-POSTINSTALL.gsub(/^\s*/, '')
+        #! /bin/sh
+        set -e
+        set -x
+        
+        service gunicorn stop
+        rm #{LINK_PATH}
+        ln -s #{INSTALL_DIR_PATH} #{LINK_PATH}
+        service gunicorn start
+        POSTINSTALL
+        postinstall.close()
+        FileUtils.chmod(0755, postinstall.path)
+
         args = ["fakeroot", "fpm", "-s", "dir", "-t", "deb",
             "--exclude=build",
             "--exclude=rakefile",
             "--exclude=.git",
             "--exclude=**/*.pyc",
-            "--prefix=/opt/wwc/mitx-#{commit}",
+            "--after-install=#{postinstall.path}",
+            "--prefix=#{INSTALL_DIR_PATH}",
             "-C", "#{REPO_ROOT}",
             "--depends=python-mysqldb",
             "--depends=python-django",
@@ -42,8 +68,8 @@ task :package do
             "--depends=python-markdown",
             "--depends=python-pygments",
             "--depends=mysql-client",
-            "--name=#{package_name}-#{commit}",
-            "--version=0.1",
+            "--name=#{deploy_name}",
+            "--version=#{VERSION}",
             "--iteration=#{build_number}",
             "-a", "all",
             "."]