#1 Children of gtkmpaned widgets are incorrectly positioned

[Ron Yorston]

Children of gtkmpaned are incorrectly positioned unless the gtkmpaned happens to be at (0,0) in its parent.

The test program doesn't show the problem because the paned widget is at (0,0).

The attached patch fixes the child offsets and changes the test program to demonstrate the problem.

[Ron Yorston]