first round of fixes

FindAwesomium and AWESOMIUM_LIBS added/fixed
OS.h include wglew.h is now guarded from *nix
removed Sigma_LIBS from cmake (unused)
ADDITIONAL_LIBS is now ADDITIONAL_GLFW_LIBS in cmake
compiles and runs on ubuntu 13.04

- glewExperimental = GL_TRUE
- X11 and other odd GLFW dependencies linked in cmakelists
spaces changed to tabs in CMakeLists
Removed ADDITIONAL_GLFW_LIBS from cmake

danix is right that building GLFW as a shared library removes the need for manually linking X libraries
also, I had missed an "awsomeium" typo. fixed.
Enabling DEPTH_BUFFER_TEST; fixes depth buffer issues
Merge pull request #69 from wrongu/depth-buffer-fix

Fixed depth-buffer problem
Merge pull request #67 from wrongu/glfw

Linux + glfw (ubuntu 13.04)