ImageMagick animators now can use extra_args

As a general solution for passing further args
to imagemagick when generating animations,
extra_args is now actually used. Extra args are
placed after all other args, but before the
output file name.

Author: erelson

lib/matplotlib/animation.py

@@ -696,7 +696,11 @@ def delay(self):
 
     @property
     def output_args(self):
-        return [self.outfile]
+        if self.extra_args:
+            args = list(self.extra_args)
+        else:
+            args = []
+        return args + [self.outfile]
 
     @classmethod
     def bin_path(cls):