Fix exception with Pillow 3

Image.fromstring was removed in Pillow 3.0.
Also added missing numpy import.

examples/pylab_examples/agg_buffer.py

@@ -4,6 +4,8 @@
 convert it to an array and pass it to Pillow for rendering.
 """
 
+import numpy as np
+
 import matplotlib.pyplot as plt
 from matplotlib.backends.backend_agg import FigureCanvasAgg
 
@@ -28,7 +30,10 @@
 X = np.fromstring(s, np.uint8)
 X.shape = h, w, 3
 
-im = Image.fromstring("RGB", (w, h), s)
+try:
+    im = Image.fromstring("RGB", (w, h), s)
+except Exception:
+    im = Image.frombytes("RGB", (w, h), s)
 
 # Uncomment this line to display the image using ImageMagick's
 # `display` tool.