In controls where a list of entries is manipulated by Add/Remove buttons

In controls where a list of entries is manipulated by Add/Remove buttons
(SSH tunnels, TTY modes, and environment variables), when the Remove button is
pressed, populate the edit controls from the entry that has just been deleted.

Several users have requested this, as it makes editing an entry easier (read-
modify-write) in the cases where order is unimportant, and also provides a
degree of undo-ability.

git-svn-id: http://svn.tartarus.org/sgt/putty@7298 cda61777-01e9-0310-a592-d414129be87e