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 -std= is
supported by both clang and gcc.
use Unix-compatible SDL include for SDL_thread
use newer boost for C++-11 compatibility
use travis ci 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 variables which aren't defined
in strict C++-11 mode. But the preprocessor variable _WIN32 seems to be defined
in all modes of MinGW.
add extra includes and preprocessor checks for _WIN32