Fix Sourcefile to only update configuration if it does not already
exist.
Update bootstrapping script to make use paklib target 'configure' for
the entire configuration process.
Update utility 'conf' to not write any data if a given key is already
set to the specified variable, saving more disk writes.
Update addpayload and Tupfile to allow 'lite' builds, creating a simple
bash script with a payload without any binary content at all, depending
on lua and git and build systems on the target system.