There is an error in my patch (already fixed in pdb-clone) and in Jyrki's patch.
Running Jyrki's patch on quit.py produces the following output where the line
number in the last entry of the backtrace is incorrect (should be line 9 instead
of line 7):

$ python quit.py
--Return--
> /tmp/quit.py(4)bar()->None
-> pdb.Pdb().set_trace()
(Pdb) quit
Traceback (most recent call last):
  File "quit.py", line 11, in <module>
    foo()
  File "quit.py", line 7, in foo
    bar()
ZeroDivisionError: integer division or modulo by zero

This problem does not occur when issue 17277 is fixed.
Meanwhile the attached patch, based on Jyrki's patch and based on the 2.7
branch, fixes this.