Admin tools development/Global CheckUser

It has been requested by numerous parties that the ability to run checkuser across multiple wiki simultaneously would enhance Stewards' ability to locate and block spam bots.

Requirements

 * current local tool exists at m:Special:CheckUser; propose extending that
 * have an addition permission bit (can be automatically granted to the Stewards group, but should be a granular permission)
 * should re-use local tool's code as much as possible to avoid code repetition/divergence

Workflow

 * On meta:Special:CheckUser, user selects "Global CheckUser" option
 * Tool uses existing (where possible) functions to run CU on local wikis
 * Results are returned to a single UI on Meta

Questions

 * Where are log entries placed?
 * Global CU log - Hard for local wikis to see the global action
 * Local CU log - Could potentially be a lot of log spam and cause many questions
 * could place in local log and identify them as global CU as an FYI
 * What does the global search results set look like? (Do we group by wiki, by action type, by IP, by day)?
 * Are smaller limits needed given the potential to slow all wikis down at once?