Show warning when file can't be accessed during extraction

[cornelius]

When running inspection on file scopes with the --extract-files option set it can happen that a file can not be accessed at the point in time when the file is extracted, e.g. when the system changes during inspection because of other running processes.

In this case the inspection should continue and create a description which is as complete as possible. Issues with file access should be reported as warnings during inspection and as list at the end of the inspection with a hint for the user what they mean and how to deal with them.

Display of descriptions should work without error, even when extracted files are not there. There should be warnings at the appropriate places to tell the user why files are missing.