Revert "Try to patch and configure postgres through ambuild"

This reverts commit 68dfc82b8eb0ce11f621af67ec247b5f47e4a189.
Update to use PostgreSQL 9.4
Move postgres preparation into seperate script

Fetching, preparing and configuring of the postgresql sourcecode
is done in a seperate prepare_postgresql.sh script now.

People can use this script for their manual builds,
if they don't want to use checkout-deps.sh.