[Bug-guile-ncurses] effects in gc handlers

[rain1]

Hello!

Somebody was having trouble with gc semantics in ncurses. They were 
asking about how to ensure X would not be garbage collected before Y. I 
believe that should never be an issue when writing scheme code.

I had a search through the docs for 'garbage':

> If that #<window> is garbage collected, the curses library cannot 
> continue.

> Procedure: delwin win
>    This function is called implicitly if a window is garbage collected.

So effects are being triggered by garbage collection. I suppose that 
this is done to try to make the library easier to use but in fact it 
cause an abstraction leak where programmers had to worry about GC 
semantics.

An alternative solution could be to define and use a form like (with-win 
(lambda (w) ...)) to abstract over the create, use, delete pattern that 
is standard in C.

I've created a patch here that removes effects from garbage collection 
handlers: 
https://github.com/rain-1/guile-ncurses-nogceffects/commit/e6cbeb6b296e5a10cf5ec34dbd18c37670bcc2db

I hope that it or at least the idea is useful to someone!