Request for review, Bug#3755, "Cannot create index on Falcon table (record memory exhausted)"

[Christopher Powers]

Hi,

Code manifestation of the "Scavenger vs DDL" discussion: 
http://lists.mysql.com/commits/63302

I did these things:

1. Moved updateCardinalities() out of the Scavenger to a separate thread.
2. Signal updateCardinalities() from the Scavenger task.
2. For load-based (unscheduled) scavenges, don't commit pending system 
transactions.
3. For scheduled scavenges, check syncSysDDL.isLocked() before 
committing pending system transactions.

Chris