Updated the task system in the example directory to support:

Cilk (cilk_for), OpenMP (#pragma omp parallel for), TBB(tbb::task_group and tbb::parallel_for)
as well as a new pthreads-based model that fully subscribes the machine (good for KNC).
With major contributions from Ingo Wald and James Brodman.

ispc.h

@@ -51,6 +51,9 @@
 #elif defined(__APPLE__)
 #define ISPC_IS_APPLE
 #endif
+#if defined(__KNC__)
+#define ISPC_IS_KNC
+#endif
 
 #include <stdint.h>
 #include <stdlib.h>