Add Django v1.5 testing support with Heroku

Store changes made in post_compile in the cache.

Remove shared db from release and add heroku-postgresql dev db

Fixing the compile hook scripts paths

The compile script is run with the root of the git repo of the project
being pushed as the working directory.

$BIN_DIR is pointing to the bin directory of the buildpack which is not
where you would want to put the pre and post compile hooks.

Changing back to the old convention of looking for the hooks from the
bin directory at the root of the project.

Use $BIN_DIR in hooks.

upgraded distribute to v0.6.36.

fixes pip v1.3.1 installation issue

Allow pylibmc to be commented out in the requirements file

/cc @alexclark