Optimization of ImageStat.Stat._getcount method

The new implementation uses "sum" instead of the construct
"functools.reduce(operator.add, ...)". Test showed that the
new function is about three times faster than the original.
Also it is shorter and easier to read.

Signed-off-by: Andreas Florath <andreas@florath.net>

src/PIL/ImageStat.py

@@ -69,10 +69,7 @@ class Stat:
     def _getcount(self):
         """Get total number of pixels in each layer"""
 
-        v = []
-        for i in range(0, len(self.h), 256):
-            v.append(functools.reduce(operator.add, self.h[i : i + 256]))
-        return v
+        return [sum(self.h[i: i + 256]) for i in range(0, len(self.h), 256)]
 
     def _getsum(self):
         """Get sum of all pixels in each layer"""