Re: html dir links, table summary

[Karl Berry]

    > I just tried generating HTML output with the current development
    > version of makeinfo and didn't get a "Prev" link on the Top file

Many documents explicitly give the pointers, as in:
@node Top, Introduction, (dir), (dir)
I suspect that's why Kurt's doc has a Prev pointer to it.

    In fact, if TOP_NODE_UP_URL is not set, there is a link to the (dir)
    node, because of TOP_NODE_UP, and the link to the (dir) node is
    transformed to an url according to the 'HTML Cross References'
    specification.

Yeah.  In practice, I think we'd better serve Texinfo users by changing
the behavior to eliminate any (dir) link if TOP_NODE_UP_URL is not set,
because no one (that I've ever seen) actually creates a dir/index.html
or dir.html file.

I propose:
- rename TOP_NODE_UP_URL to DIR_LINK_URL (keep old name for
  compatibility, with exactly the same meaning).
- make its value replace (dir) wherever it appears, implicitly or explicitly.
- if it's not set, generate nothing at all for such pointers in the HTML
  output.

Wdyt?

K