Minor compilation fixes and setting the number of threads for openmp

As you already know, ncpus does not control the number of threads for those parts of graphlab that use openmp. This is a quick fix for that. 

I found several errors when compiling the complete code base and added fixes to some of them (includes in fiber_control.hpp and hopscotch_table.hpp and a change in the URL of openCV in Sourceforge). The includes   fixes problems which are resposibility of the boost libraries, but since they can be easily fixed from graphlab, I did. 

Still, there is an issue since quite a while when compiling the graph_analytics toolkit. It seems to come from one of the Spirit includes. I do not know how to fix that one.