Log errors in thumb.php

Authored by Tgr.


Log errors in thumb.php

Add new streamFileWithStatus() methods to FileRepo and
MediaTransformOutput that can be used to get more detailed error
information on failure. The historic streamFile() methods become sinple
wrappers to the new methods. Thumb.php is changed to use the
streamFileWithStatus() methods so that failure reasons can be logged.

Change-Id: I3088cde2044a7ff00841e53ca252d0b222c8b518