Improvement to zoom functionality
Detail: Previously, when using Ctrl + scrollwheel to zoom out it's possible for the window to shrink and no longer lie under the mouse, meaning you have to keep chasing it around the screen. The code now attempts to keep the same pixel under the mouse pointer first with the scroll bars and then by moving the window if that's insufficient, but it avoids moving window furniture off the edges of the screen. Zooming initiated by keyboard, mouse wheel or magnifier keeps the window the same size and shape whenever possible. Zoom in coarse steps in the form x:1 or 1:x is now possible by Ctrl-Shift-resize. Admin: Ref https://www.riscosopen.org/forum/forums/8/topics/2146?page=21#posts-99304 Submmission for Paint bounty.