bug#7015: Documentation of `mouse-drag-copy-region'

[Arni Magnusson]

Today I discovered that selecting a region with the mouse automatically 
copies the region, altering the kill ring. I guess I don't use the mouse 
much, but I was expecting mouse dragging to select passively like shift 
arrows.

It took me a few minutes to find the simplest way to disable this 
behavior, by setting the `mouse-drag-copy-region' variable to nil.

I suggest the `mouse-drag-copy-region' variable should be cross-referenced 
in the `mouse-set-region' docstring, to shorten the path of discovery. 
Then it would only take C-h k drag-mouse-1 to find out about this 
variable.

Cheers,

Arni