csync_exclude: Use PathMatchSpecA instead of PathMatchSpecW

csync_exclude: Use PathMatchSpecA instead of PathMatchSpecW

So we avoid lots of memory allocation.
We can work with char* directly since both the pattern and the file
name are in UTF-8 and there is no need to understand unicode for
such pattern.

(In fact, '?' would not match anyore non-ascii characters, but I
don't think that's a problem. I don't think anyone use '?' in its
exclude list. And the two allocations per call to csync_fnmatch are
really worth getting rid of)