soon as GET-CHARACTER returns any character at all that was
previously read. This makes the continuation prompt appear
properly for partial expressions. Thanks to Neil Jerram!
Dynamically link libguilereadline.so.
(readline): Just define in this module, do not overwrite builtin
variable. The builtin readline function is now named "%readline",
so this works. See below.
(activate-readline): New function which contains the readline
activation code formerly found in top-repl.