Boost

This is in addition to #162. While struggeling with an agressive autocompletion I did changes to enable boost::signals2 (starring at the compiler warning for too long) and fixed libclang completion with boost 1.57 (Arch Linux updated a week ago and it was gone). I am not sure why the include fixes are required, since RStudio does build with 1.57. I will check this with another computer once I am at home.

Regards
Marvin