[release blocker] use node.title (resp users.name) in Views argument summaries

Working on it.

Attached patch adds the two missing D6 behaviors - display node title (resp user name) instead currently of nid (resp uid) :
- in arguments summary lists (relies on the 'name table' and 'name field' properties used by the default views_handler_argument handler)
- in title '%n' placeholders (relies on a custom references_handler_argument handler)

But, after much head-scratching, I only manage to have the 'arguments summary' part work by patching views to fix a possible bug there. I'll post the patch in the Views queue and ask for feedback over there.

Also, the references_handler_argument handler introduced here is common to both noderef and userref, and thus needs to be exposed at a higher level (in D6, such handlers were exposed by content.module).
Therefore, the patch introduces references.module as a wrapper for common functionnality. Other views handlers or plugins will need this too.

No commitment on the actual rate to which bits of 'similar' code from noderef and userref will be refactored and factorized out into references.module in the future, but at least the door is open.

Views issue + patch : #1059646: Argument summaries : 'title table' not correctly joined ?

fix whitespace styling error

Rerolled after #962694: [release blocker] Make Node Reference Relationships Work in Views and #1046886: [release blocker] Use the 'many_to_one' views filter handler

#1059646: Argument summaries : 'title table' not correctly joined ? got fixed in Views dev, so the patch now works fine (retested).
Committed (1st d.o git commit, at last !).