M IOBinding.py
M PyShell.py

* Could not remove last set of saved breakpoints from a file
* Starting with empty edit window, could not load a file
* Multiple adjacent breakpoints were saved as one breakpoint
* Storing breakpoints whenever a file is closed can get them out
  of synch with the saved version of a file.  Only store them when the
  file is saved.
* Add comment on current limitations on file editing in the presence of
  breakpoints.
* Replace get_current_breaks() with update_breakpoints(), add an update to
  PyShellEditorWindow.breakpoints, which is the master breakpoint data
  structure, and which is used to reload the subprocess debugger.
* Revert Debugger.Debugger.load_breakpoints() to use editwin.breakpoints.
  It is easier to debug the debugger if the breakpoint list in IDLE is
  identical to the list in the subprocess debugger and is transferred when
  the subprocess debugger is restarted, because this list can be easily
  queried.
* Cleanup some linespacing and comments in IOBinding.py