revision 1.4 of CallTipWindow.py

SF bug 546078:  IDLE calltips cause application error.
Assorted crashes on Windows and Linux when trying to display a very
long calltip, most likely a Tk bug.  Wormed around by clamping the
calltip display to a maximum of 79 characters (why 79? why not ...).

Bugfix candidate, for all Python releases.