Improved timer implementation The new timer model is formalized as using a separate thread to handle timer callbacks. This was the case on almost every platform before, but it's now a requirement, and simplifies the implementation and makes it perform consistently across platforms. Goals: * Minimize timer thread blocking * Dispatch timers as accurately as possible * SDL_AddTimer() and SDL_RemoveTimer() are completely threadsafe * SDL_RemoveTimer() doesn't crash with a timer that's expired or removed

define(AC_CHECK_DEFINE,[dnl
  AC_CACHE_CHECK(for $1 in $2, ac_cv_define_$1,
    AC_EGREP_CPP([YES_IS_DEFINED], [
#include <$2>
#ifdef $1
YES_IS_DEFINED
#endif
    ], ac_cv_define_$1=yes, ac_cv_define_$1=no)
  )
  if test "$ac_cv_define_$1" = "yes" ; then
    AC_DEFINE([HAVE_$1],[],[Added by AC_CHECK_DEFINE])
  fi
])dnl
AC_DEFINE([HAVE_$1],[],[Added by AC_CHECK_DEFINE])