xboard: how to enter variations

[Charles Blair <c-blair@illinois.edu>]

   I type
xboard -variations true

and the board display pops up.  In edit game
mode, I make the
moves 1 e4 e5 2 Nf3 and it waits for Black's move.

Then I use the < button to go back one move.
I hold the shift key while moving a pawn from
f2 to f4.  Then I save the file.  It shows
2 f4 as a second game, instead of a variation
in the first game.