[Common] Drop boost::asio in favor of pure asio.

This change allows to build cocaine runtime with libboost 1.46 and do not break Ubuntu Precise support with system boost libraries installed.

Also, at last we are now using std::error_code and categories instead of deprecated boost::system::* analogs.
[Common] Using pure asio in benchmarks too.
Merge pull request #145 from 3Hren/maybe-asio

[Common] Drop boost::asio in favor of pure asio.