Adds UDUNITS to coi-services

# Buildout Required

This merge will require a buildout to be performed by developers. 

We have had some Undefined Symbol errors on Linux systems.  This stemmed from the fact that the `udunitspy` library wasn't linked with `libexpat` which is the XML parsing library the `libudunits2` uses to parse XML files. I updated the library to include `libexpat` but I can't regenerate the problem on my local linux boxes, this is indicative of the problem being resolved but I'm using `ubuntu` and CentOS has it's own issues.  I verified that the buildbot VMs that I have access to are good to go but other developers will need to verify.

# ImportError

If you experience an `ImportError` with the undefined symbol, please let me know as soon as possible so I can try to fix it.  This simple patch has been an incredibly tedious task to ensure cross-platform compatibility and I want to ensure that it's complete.

Thanks~