WL#3089: Refactoring for multi-source and info system tables

Affects: Server-7.1   —   Status: Assigned   —   Priority: Medium


Take refactoring parts of the WL#1697 Multi-source code (that have
already been agreed with/preliminary reviewed by Mats and Guilhem),
port it to MySQL version 5.2 and push it.


Doing this first step will
1. make the code easier to maintain
2. make multi-source easier to implement, 
3. make info system tables be easier to implement.
Since this is only refactoring and it has been discussed/reviewed 
before, I hope no long descriptions are needed and we can instead 
study the patches.