Clean up log.debug() usage

See the forum thread for discussion of the heavy debug logging that goes on during AS startup.

This is a parent JIRA for a general cleanup; the real action items will be sub-tasks. I'll create a subtask for some general profiling work, and we can add subtasks for cleaning up specific areas (external projects or chunks of code in the AS codebase itself.)

Cleanup consists of:

1) Convert overly spammy DEBUG logging to TRACE. When you convert it, preferably make it a log.debugf statement; otherwise add a guard unless the message is static.
2) Try and identify remaining debug log messages where the cost of constructing the message is high.
3) For such messages, either convert to log.debugf or add a log.isDebugEnabled() guard.