Use non-strict-ansi mode to build sources

Switch back to gnu++0x until the source can be compiled in strict ansi mode
with MinGW and Travis CI supports C++11 for GCC/Clang. This is -std is
supported by both clang and gcc.
Use Unix-compatible SDL include for SDL_thread
Use newer boost for C++-11 compatibility
Enable Travis CI build with clang
Use different swprintf call for _GLIBCXX_HAVE_BROKEN_VSWPRINTF
Use more widely used preprocessor defines for MinGW

The code still uses a lot of WIN32 preprocessor variable which aren't defined
in strict C++-11 mode. But the preprocessor variable _WIN32 seems to be defined
just fine and is used now everywhere in the code.
Add extra includes and preprocessor checks for _WIN32