Utility benchmarking macros

This new macros could be used to benchmark overall
execution time of some chunk of code, running in cycle.

The usage is:

  void foo(void) {
    TIMEIT_BLOCK_INIT(overall_bar);

    for (...) {
      ...

      TIMEIT_BLOCK_BEGIN(over_bar);
      bar();
      TIMEIT_BLOCK_END(oberall_bar);

      ...
    }

    TIMEIT_BLOCK_STATS(overall_bar)
  }


  This would print total time which was spent on
  running function bar().

--
svn merge -r58281:58283 ^/branches/soc-2013-depsgraph_mt

source/blender/blenlib/PIL_time.h

@@ -87,6 +87,26 @@ void    PIL_sleep_ms(int ms);
 		TIMEIT_END(id);                                                       \
 	} (void)0
 
+#define TIMEIT_BLOCK_INIT(what) \
+	double _timeit_var_##what = 0; \
+	(void) 0
+
+#define TIMEIT_BLOCK_BEGIN(what) \
+	{ \
+		double _timeit_block_start_##what = PIL_check_seconds_timer();  \
+		{ (void)0
+
+#define TIMEIT_BLOCK_END(what) \
+		} \
+		_timeit_var_##what += PIL_check_seconds_timer() - _timeit_block_start_##what; \
+	} (void)0
+
+#define TIMEIT_BLOCK_STATS(what) \
+	{ \
+		printf("%s time (in seconds): %f\n", #what, _timeit_var_##what); \
+		fflush(stdout); \
+	} (void)0
+
 #ifdef __cplusplus
 }
 #endif