Address Sanitizer

[Seadragon91]

Because of any issues in cuberite, I bump this up.

Have found this and it looks interessting.
https://code.google.com/p/thread-sanitiz.../CppManual

This requires at least clang 3.2. I think adding a build option with the flag

Code:

-fsanitize=thread -fPIE -g -O2

would be a good idea. Had tested this yesterday and @worktycho had already a look on it. I compiled cuberite with it and have a few stack traces on my account
https://gist.github.com/Seadragon91