Resizing hash tables in Guile

[Mikael Djurfeldt]

I've just committed resizing hash table functionality to the Guile
core hashtable functions (in hashtab.c).

Currently, the only thing which has changed in the API is that the
size argument to the hash table constructors is now optional.  If
omitted, you get a resizing table.

Please comment on this API and also take a look at the implementation
in hashtab.c.

Questions:

Is this a good thing?  Should we keep it?

I made the hash tables thread-safe (locking/unlocking a mutex at hash
table access and rehashing).  Is that good?  An alternativ is to
require of the programmer to make sure the hash tables aren't accessed
in parallel.

The implementation isn't quite finished.  Removal should be rewritten
for the new tables.  Also, weak hash tables need to be handled in
hashtab.c in order to maintain a correct item count.

M