choosing specified cache slot for xcache_set

[digi1]

I would like to suggest an optional paramter for xcache_set to specify a certain variable cache (var#0, var#1 etc).

For me and maybe others it would be very useful, because I am caching one information object that is very large and many small ones. If I were able to specify the variable cache, I could ensure that the
large object and the small objects stay in different caches. Otherwise the small objects may end up in positions, so that there is not enough continuous room left for the large object.