* Added $wgDebugLogPrefix, to allow users (or in this case, multiprocess command...

* Added $wgDebugLogPrefix, to allow users (or in this case, multiprocess command-line scripts) to set a debug log line prefix
* Improved blob_tracking.sql docs
* Allow testCompression.php to run until happy instead of a specified revision count
* Added docs for some debugging globals in DefaultSettings.php

In experimental script recompressTracked.php:
* Fixed crippling bugs, seems to work now. Needs more testing.
* Improved usage documentation
* Use DiffHistoryBlob by default if available
* Set a process-specific log prefix, added more debugging output
* Optimised commit() slightly by merging the locking read queries using IN()
* Fixed finishIncompleteMoves() so doPage() acts on only that page. Also run finishIncompleteMoves() for orphan lists.