Jordan Russell's patch (3rd of several). We now don't call TermOut()

Jordan Russell's patch (3rd of several). We now don't call TermOut()
if the PuTTY window has the mouse capture (i.e. a drag-select is in
progress). This means you can drag-select at your leisure without
the screen contents wandering around providing you with a moving
target. Likewise dragging the scrollbar to find a piece of history
in the scrollback.

git-svn-id: http://svn.tartarus.org/sgt/putty@1517 cda61777-01e9-0310-a592-d414129be87e