New node_attributes facility and table.

Auxiliary node attributes, such as service tag #, BIOS version, etc., are
should now be placed into the node_attributes table.  This can be accomplished
by either using the node_attributes command line tool, or by using the
modnodeattributes_form.php3 form (not linked in anywhere yet, but will be
in a moment).  Attribute names and values are checked for sanity using
table_regex entries.  Also note that I started with the nodecontrol stuff
as a template.

The command line tool and web form (which simply calls the command line tool
to actually do the modifications) can add, delete, and/or remove attributes.

Finally, note that the bios_version column has been moved from the nodes
table to the node_attributes table.  The Node Information page will show
the list of current attributes at the bottom of the info table.