include SDL_opengles2.h instead of SDL_opengles.h
Merge pull request #36 from krnlyng/gles

include SDL_opengles2.h instead of SDL_opengles.h
Use non-strict-ansi mode to build sources

The sources don't allow to be build in strict ansi mode. Thus the change from
GNU++11 mode to C++11 in 6a46ad138c02138bb8f9a425afdec149bfa39182 made building
the sources impossible. This was also catched by Travis CI but ignored by the
author and merged anyway.

Revert this change until the source can be compiled in strict ansi mode and
Travis CI support C++11.
use correct SDL include for SDL_thread
Fix swprintf call for _GLIBCXX_HAVE_BROKEN_VSWPRINTF

339ca50a57364b2509a6b5e7a073698038096a4d broke build with GCC for Windows for
code which was specific to windows. This should have never been mixed with
clang specific hacks.

Just split this call in a clang and a _GLIBCXX_HAVE_BROKEN_VSWPRINTF specific
implementation.
Use never boost for C++-11 compatibility
Enable travis ci for clang