Minor bug in examples/object_picker.py, with a patch

There is a minor bug in the object_picker.py example. On the 2nd and
subsequent times a line is "picked", if the marker style had been
changed previously, the original marker choice "None" no longer appears
as a choice in the marker menu. I.e. there is no way to turn off a
previously selected marker.

Below is a (one line) patch that fixes this.

  -Al

···

--
Al Schapira <a.d.schapira@...107...>

*** /usr/local/matplotlib-0.51/examples/object_picker.py
2004-02-26 15:22:58.000000000 -0500
--- object_picker.py 2004-03-09 16:50:36.000000000 -0500
***************
*** 151,157 ****
          marker = line.get_marker()
          if marker is None: marker = 'None'
          styles = [marker]
! for key in lineMarkers.keys():
              if key == marker: continue
              styles.append(key)
   
--- 151,157 ----
          marker = line.get_marker()
          if marker is None: marker = 'None'
          styles = [marker]
! for key in keys:
              if key == marker: continue
              styles.append(key)