Add comma groupings to timeit magic loop count

IPython/core/magics/execution.py

@@ -92,16 +92,14 b' class TimeitResult(object):'
                 pm = u'\xb1'
             except:
                 pass
-        return (
-            u"{mean} {pm} {std} per loop (mean {pm} std. dev. of {runs} run{run_plural}, {loops} loop{loop_plural} each)"
-                .format(
+        return "{mean} {pm} {std} per loop (mean {pm} std. dev. of {runs} run{run_plural}, {loops:,} loop{loop_plural} each)".format(
                     pm = pm,
                     runs = self.repeat,
                     loops = self.loops,
                     loop_plural = "" if self.loops == 1 else "s",
                     run_plural = "" if self.repeat == 1 else "s",
                     mean = _format_time(self.average, self._precision),
-                    std = _format_time(self.stdev, self._precision))
+            std=_format_time(self.stdev, self._precision),
                 )
 
     def _repr_pretty_(self, p , cycle):