[patch] interruptible search in the viewer

[Roland Illig]

Jindrich Makovicka wrote:
> The attached patch makes the search function interruptible by Ctrl-C.

Committed. Thanks.

> I am not sure it it doesn't interfere with get_byte() stuff which can
> do some I/O, but block_search doesn't disable the interrupts during
> I/O either.

I just fixed the case when using mc_read(). The other cases still need 
to be checked.

Roland