bug#41156: 26.3; 27.0.91; linum-mode interferes with xterm-mouse-mode

[Neil Okamoto]

You cannot drag the vertical boundary between windows to the right, if the 
righthand window has linum-mode active. I’ve confirmed this on Emacs 26.3 and 
27.0.91. I have not tried earlier builds.

Steps to reproduce:

$ emacs -nw -q
    M-x xterm-mouse-mode
    C-x b *scratch*
    C-x 3

    Use the mouse to drag the vertical divider right and left? Succeeds.

Now enable linum-mode:

    M-x linum-mode

    Use the mouse to drag the vertical divider left? Succeeds.
    Use the mouse to drag the vertical divider right?
    Fails with the message "<left-margin> <mouse-movement> is undefined"


Thank you-