M Debugger.py
M EditorWindow.py
M PyShell.py

0. Polish PyShell.linecache_checkcache()
1. Move break clearing code to PyShell.PyShellEditorWindow from
   EditorWindow.
2. Add PyShellEditorWindow.breakpoints attribute to __init__, a list of
   line numbers which are breakpoints for that edit window.
3. Remove the code in Debugger which removes all module breakpoints when
   debugger is closed.  Want to be able to reload into debugger when
   restarted.
4. Moved the code which sets EditorWindow.text breakpoints from Debugger
   to PyShell.PyShellEditorWindow and refactored.
5. Implement reloading subprocess debugger with breakpoints from all open
   PyShellEditorWindows when debugger is opened or subprocess restarted.
6. Eliminate the break_set attribute, use the breakpoint list instead.