Volker Ruppert 7fd9194d81 Implemented lock mechanism for hard disk images (fixes SF bug #605).
- Create a file with image name plus extension ".lock" if an image is opened
  in read/write mode. This file will be deleted after closing the image.
- Check for a lock file before opening an image and fail if it exists.
- Check for a lock file before creating a undoable/volatile redolog file and
  fail if it exists.
2017-01-30 19:08:37 +00:00
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