wishlist: incorporate EVERYTHING permission with (or where) usr_has_perm_at

[Andrea Neiman]

Related discussion on bug 2024657.

The problem, today (3.12 main) and shamelessly copied from my slides:

* The usr_has_perm_at function doesn't consult the EVERYTHING permission, since it would execute the EVERYTHING permission check as "Give me ALL THE PERMISSIONS for ALL THE LOCATIONS for this user!" and that would be a huge data dump up to whatever part of the software is looking for this info.

Potential solutions, in need of discussion, similarly copied shamelessly:

* Identify where usr_has_perm_at is in use, and add a separate EVERYTHING check to those areas
* Teach usr_has_perm_at to check EVERYTHING but do something reasonable (i.e., not dump all that data).
* Other suggestions?

Discuss!