Do not create a temporary string (it slows down writing windows)

Author: jonwright

fabio/edfimage.py

@@ -593,7 +593,7 @@ def get_edf_block(self, force_type=None, fit2dMode=False):
 
         # Then update static headers freshly deleted
         header_keys.insert(0, "Size")
-        header["Size"] = len(data.tostring())
+        header["Size"] = data.nbytes
         header_keys.insert(0, "HeaderID")
         header["HeaderID"] = "EH:%06d:000000:000000" % (self.index + fit2dMode)
         header_keys.insert(0, "Image")