Use address-based hashing functions for Internal hash tables

[qinsoon]

mmtk/julia@a933faa introduced address-based hashing functions to the interface, and the code in object ID uses those functions.

Julia also has its internal hash table. We currently use PTRHASH_PIN and OBJHASH_PIN to pin values that are inserted into the internal hash table. We would like to use the new functions to properly deal with those hashed pointers so we don't need to pin them.

The goal is to remove PTRHASH_PIN and OBJHASH_PIN and allow those objects to be removed. However, it is unclear how much improvement we expect to see from these changes.

[d-netto]

We should start by instrumenting PTRHASH_PIN, PTR_PIN and collecting a pinning profile, to see if this is actually a bottleneck.

Will try to take a stab at it.