Re-Introduce -Wall, add -Wextra and fix all warnings

- fix all **int vs uint** warnings
- fix gcc **aliasing warning** in ProxyClass.hpp
- fix **comment-in-comment** warnings
- add **-Wall** for icpc and g++
- add **-Wextra** for g++
- ignore **unknown pragmas** for g++ (i.e. nvcc's pragma unroll)
- add experimental **ICC 12.1** and **PGI 13.6** support