curses mouse right-click

curses mouse right-click

Right button is button3 rather than button2.  Accept either and treat
both as "not left" to pass CLICK_2 back to the core.

Treat <Ctrl>+left-click as "not left" too, to simplify usage with Mac
one-button mouse (where <Ctrl>+left-click can be configured to send
"secondary click" but might not be set do so) or one-button laptop
trackpad (where having two fingers on the scrolling portion of the pad
while clicking the button is necessary to send "secondary click").