Mac Installer should handle upgrades / installs without explicit uninstall

Today, upgrades on Mac require a user to explicitly stop and uninstall Couchbase Server and then manually delete one or two directories in order to install a new version.

> rm -rf ~/Library/Application\ Support/Couchbase
> rm -rf ~/Library/Application\ Support/Membase

Can this manual cleanup be handled by the installer so that the user no longer has to do it?

The issue is that users don't always read the docs, especially for simple things that they expect to "just work". Fixing this might also simplify automation.