Several amends in accordance with per-thread-logging.

1. add interface processSingleLog(LogFileIndex) to LogProcessor.
2. trace slice supports multiple log files processing:
   RecordFinder stops processing after finding the first log including alias,
   then TraceSlicer processes the single log found by RecordFinder.
   Maybe we no longer need RecordID input option for TraceSlicer?
3. add TraceSlicer as the first step of reduction.
4. track CurrentFunction to get all related function calls in reduction mode.
5. minor fix in MissingAliasClassifier and TraceSlicer.