[development] Pathauto scaleability - path column in node / user table

[Gabor Hojtsy]

Karthik wrote:
>> Not all aliases in the url_alias table are nodes, and hence we cannot
>> have a "nid" column.
> 
> The id column can be an index with default 0 for non-nodal rows or
> something similar.

And for users?

Goba