Hello all,

When looking through the different hash table implementations available 
(Guile, SRFI-69, and RNRS) I found a useful SRFI-69 procedure that had 
no equivalent in Guile's native hash table API: alist->hash-table.

This patch is an attempt to add that. It works for all four types of 
hash tables: equal?, eq?, eqv? and custom.

- Dave