PATCH: use hashval_t in tree.h

[Roger Sayle]

On Tue, 9 May 2006, Ben Elliston wrote:
> 2006-05-09  Ben Elliston  <bje@au.ibm.com>
>
>         * tree.h: Include "hashtab.h".
>         (iterative_hash_expr): Use hashval_t in its prototype.
>         * Makefile.in (TREE_H): Add $(HASHTAB_H).

This is OK for mainline.  Thanks.

Roger
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