*gensym-counter* is not thread safe

[drmeister]

Fix this

[Bike]

Doing this would require either locking or fetch add of a symbol value, except the latter wouldn't really work if *gensym-counter* is a bignum. Not that that's likely.

However, the number doesn't particularly matter. Even if two calls to gensym in different threads read the same *gensym-counter*, they'll make distinct uninterned symbols. So I don't think this is a big deal.