llvmpipe: add support for nested / overlapping queries

llvmpipe: add support for nested / overlapping queries

OpenGL doesn't support this but d3d10 does.
It is a bit of a pain as it is necessary to keep track of queries
still active at the end of a scene, which is also why I cheat a bit
and limit the amount of simultaneously active queries to (arbitrary)
16 (simplifies things because don't have to deal with a real list
that way). I can't think of a reason why you'd really want large
numbers of overlapping/nested queries so it is hopefully fine.
(This only affects queries which need to be binned.)

v2: don't copy remainder of array when deleting an entry simply replace
the deleted entry with the last one (order doesn't matter).

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>