app, libgimp: commit files generated by PDB docs change
app: make sure image windows end up on the intended monitor

In gimp_image_window_new(), place the window on the right
monitor manually if we are not in single-window-mode.

In gimp_image_window_switch_page(), make sure we don't use an
unrealized new window's monitor for updating the session info, because
the monitor of an unrealized window is always where the pointer is.
devel-docs: more TODO items for GIMP3-API-Changes.txt