Revert heading change from 06752a03d, centralize the URL spec

There were several broken links referring to the old way of doing
things, and help/support sounds better anyway. Reverting with added
comments and whatnot
Fix incorrect handling of custom relationship conditions containing literals
First step to add some sanity to _resolve_condition

The original problem starts here:
 <mst> oh, yeah, I just used to check ref and randomly swap things
 <mst> it worked for enough years :)
 <ribasushi> I will be forwarding you my psychiatrist bill

READ DIFF AT YOUR OWN RISK

Over the years _resolve_condition has accumulated 3 (or 4, or 5, depends
how you look at it) distinct call-modes. None having anything to do with
another. Also it is a hot method, holding crucial functionality, which
of course means that currently at least 3 projects on CPAN are using it,
despite the private attribute. Which in turn means couple more orders of
magnitude of users on the DarkPAN. Thus just killing this method
outright *without a replacement* is not an option.

A from-scratch replacement in the face of only one person currently
*barely* understanding this codepath is a scary proposition.

Instead create an elaborate (and scarily complete) shim to proxy to a
new method holding all the logic (with the idea of making it an official
API in the coming commits).

There are no changes to any other codepaths, as this is how we ensure that
the shim is sane, and works. Next step is to erradicate all cases of the old
call in the current codebase (while leaving the sub/shim intact)/

Now let's see if we can fix CampusExplorer's bugs first...
Adjust error messages - joinfrees can be returned from noncode rels
Centralize custom rel args check, be more thorough
Rename (with a silent compat shim) couple of badly named customcond args

foreign_relname makes absolutely no sense - it *is* a relationship after all,
of course it has a name. Now renamed to rel_name to be consistent with
the relationship condition resolver

self_rowobj uses the old rowobj nomenclature - switch to self_resultobj
Pedantry - settle on rel_name vs relname, consistency throughout

Only outlier is relname_to_table_alias, which should have never existed
in the first place. Punting deprecation/etc cycle until future Oracle
work... sigh
Add foreign_resultobj to the customrel signature

Tests in next commit
Add (now passing) tests for set_from_related() via 'foreign_resultobj'