WIP: preloading of ispell dictionary

Hello

I wrote some small patch, that allow preloading of selected ispell
dictionary. It solve the problem with slow tsearch initialisation with
some language configuration.

This patch is most simple - simpler than variant with shared memory
and it is usable on Linux platform.

I registered some issues about access to different king of memory :(.
The local memory is the best, than shared_memory and then virtual
memory. Queries with preloaded dictionary are about 20% slower (but
still good enough). It depend on platform (and language sure) - I
afraid so this module doesn't help on MS Windows.

Tested on 64bit Fedora Linux - probably on 32bit these issues will be smaller.

I would to add this patch to next commitfest.

can somebody test it for different platforms and different languages than Czech?

Regards
Pavel Stehule