For review: Scavenger, backlog and memory param changes

[Christopher Powers]

Kevin, these are mostly Scavenger fixes.


Bug #42424, "Serious performance degradation after new scavenger"
- The one-line Scavenger fix is now many more lines. See the bug for 
details.

Bug #42505, "Falcon: Record backlogging not enabled by the Scavenger"
- Backlogging was broken. Not any more.

Bug #42510, "Falcon: Default memory parameters must be changed"
- Per the email thread last week

Bug #36442, "Falcon: crash during optimize table"
- This is the bug that's caused all the trouble: Scavenger + Optimize + 
Param fixes


With these fixes, I can now run the testcase for Bug#36442 to completion 
using the default memory parameters. Note, however, that 
Index::optimize() still needs to be rewritten using the IndexWalker.

Chris