Conservation Tracking dependencies and fixes for building with GCC on Linux and Mac

This pull request contains various fixes to enable compilation of ilastik and its dependencies, including those needed for conservation tracking.

Successfully builds on:
* Ubuntu 14.04 using GCC 4.8
* Ubuntu 12.04 using GCC 4.7
* Mac OSX 10.9 using Homebrew's GCC 4.8
* a OSX 10.8 build is currently running

Most fixes are unrelated to Conservation Tracking and include:
* adding the pythonpath to `BUILDEM_ENV_STRING`
* fix openssl building on Ubuntu 14.04 - had Perl incompatibilities
* CPLEX path hints for Ubuntu
* boost, vtk and python patches for OSX

Important for Conservation Tracking:
* added mlpack and armadillo as dependencies
* armadillo currently needs OpenBLAS -> `-DWITH_ATLAS=0`
  * OpenBLAS builds fine on the aforementioned OSes
* add boost random
* update `pgmlink.cmake`

In kind collaboration with @martinsch