Daniel's modifications to Tim's LP-BRIM in R

There are a few minor changes (that my version of R balked at or a library that wasn't otherwise loaded), one utility function (that probably exists in some other network-specific package), and one major change to the core LP-BRIM code that provides a **ginormous** optimization.

Some quick and dirty speed checks indicate that the code is now at least ~100-1000x faster, and the improvement is potentially quadratic with the number of nodes in the network.