[TASK] Raise severity for stale lock file

To make debugging this easier and as a stale lock file really
represents an error in the locking mechanism the severity
being used for logging stale lockfiles should get raised.

This applies to the old locking API only.

Change-Id: I94b91d10411e60bfe944445865f5cb630e988701
Resolves: #67227
Releases: master, 6.2
Reviewed-on: http://review.typo3.org/39871


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Benjamin Mack <benni@typo3.org>