Using fixed width integer types

[riffard]

Modern C++ requires to use of the fixed-width integer types that were introduced in C++11. It's recommended to use int64_t instead of long int. The header is cstdint: documentation.

[tunnell]

These are good suggestions. If it's quick, you have a better feeling for C++11 than we do, so you're welcome to try your hand at a PR that we can test to make sure things function fine. Right now NEST is maintaining more than developing, so this will happen but probably slowly.

[mszydagis]

I have fixed this today, didn't take long thanks to grep, Quentin and Chris -- Will be uploading later tonight, combining with the other minor issues. I even went one step further and changed all unsigned long or unsigned long int's to uint64_t