The + typed character can only be generated on English keyboards by
shift-equals, resulting in a failure to recognize ctrl-plus because of
the unexpected shift modifier. Adapt by supporting English and Spanish
keyboards, as well as number pad keys.
Closespabigot/contikix#2
Reference: http://forums.oracle.com/thread/1356291
Signed-off-by: Peter A. Bigot <pab@pabigot.com>