[CMake] CMakeifying Boost

[Amitha Perera]

And I'll chime in that I've CMakeified the boost threading library,
and it was pretty trivial. I put the header files in one place, and
listed all the .cpp files in libs/thread/src into a library target. I
changed config/user.hpp to define BOOST_ALL_NO_LIB to supress their
library version autodetection. I think that was it.

My feeling is that most, if not all, of Boost does not require
pre-build configuring. They figure everything out at compile time
using template and preprocessor magic.

For example, compiling the threading library without providing
-pthread gives you a nice error at compile time saying "please supply
-pthread".

It's magic, I tell you.

Amitha.