[2/10] introduce a block iterator

[Tom Tromey]

>>>>> "Tom" == Tom Tromey <tromey@redhat.com> writes:

Tom> This patch prepares the way by introducing a block iterator, which is
Tom> used in preference to the dictionary iterator in most places.  The
Tom> exceptions are places which need to understand the underlying structure
Tom> of the symbol tables.

This one also did not change.
I'll be checking it in shortly.

Tom