Option mouse_buttons=3 to avoid middle mouse button conflict?

[FrodeSolheim]

BastyCDGS: Found another bug with clipboard sharing:Trying to release input grab with middle mouse button also triggers pasting from clipboard.

FrodeSolheim: The solution might be to introduce a mouse_buttons=3 option. Without it FS-UAE uses the middle button exclusively (cannot be used for pasting or other purposes) and with it, you need to use the keyboard to release the input grab.