Fixed several bugs reported by Greg McFarmane:

Fixed several bugs reported by Greg McFarmane:

 *  The invoke methods of the three Tkinter widgets Button,
    Checkbutton and Radiobutton should return the value returned by
    the callback, (like the Menu widget does):

	def invoke(self):
	    return self.tk.call(self._w, 'invoke')

 *  The select_from method of the Canvas widget should use 'from', not
    'set':

	def select_from(self, tagOrId, index):
	    self.tk.call(self._w, 'select', 'from', tagOrId, index)

    Currently, if you use select_from, you get the error message:
 'TclError: bad select option "set": must be adjust, clear, from, item, or to'

 *  The 'entrycget' and 'type' methods of the Tk menu widget are
    missing from Tkinter.

 *  There is a bug in grid_columnconfigure and grid_rowconfigure.  For
    example, this should return the current value of the 'minsize'
    option for column 0:

	f.grid_columnconfigure(0, 'minsize')

    Instead it returns the same as:

	f.grid_columnconfigure(0)

    I suggest that the hint given in the comment in the
    Tkinter.Misc.configure method should be followed - "ought to
    generalize this so tag_config etc.  can use it".  Repeating the
    same configure code several times in Tkinter is inviting errors.
    [I did not follow this advice --G]

 *  The grid_slaves method should handle options.  Currently, to pass
    options to the grid_slaves method, you have to do something like:

	grid_slaves('-row', 1)