A couple of minor improvements to the generic hash tables:

A couple of minor improvements to the generic hash tables:

o  Comment on HASH_GIVE_ALLOC corrected, the automatic choice between
   normal and pooled allocation was never implemented, because we don't
   have enough information to decide the right pool size. HASH_AUTO_POOL
   has been implemented instead.
o  Pooled allocation no longer conflicts with remove/delete, it just
   produces memory leaks within the pool, which are usually harmless.
o  Added HASH_TABLE_ALLOC switch.
o  Internal decisions to enable HASH_CONSERVE_SPACE were made too late
   and didn't influence hash node layout. Fixed.