explicitly add STATIC keyword to iris_lib target

This fixes a bug where CMake tries to link the Iris binary
to the shared lib version of iris_lib (which doesn't exist).
Merging pull request from Andre and now linking exe against static lib
Building in support for both boost filesystem v2 and v3 - permits the use of boost versions < 1.46 (as currently available on E100 naster image)
Merge pull request #1 from softwareradiosystems/master

Updating branch from srs core master