Simplifying how build works

Getting into the code to work on a possible patch I made some changes to simplify how the build works. You can now build all targets with just two params:

ant -Dhadoop.dir=... -Dpig.dir=... jar

Or similarly from make. The other params now have sensible defaults.

I changed the sub-project to create the jars under their build dir by default, instead of the root directory. I also added error messaging if required params are missing or invalid.