Fix for issue 6048, where an apparent race condition occurs when concurrent filesystem caches try to clear expired items. To avoid this causing an exception for a user session, arrange for Filesystem::clearExpired to trigger a 'clearExpired.exception' event. This should give the same functionality as currently exists. Also, have the ExceptionHandler plugin listen for the clearExpired.exception event, and suppress it as per other exceptions.
clean up whitespace which caused php_cs to fail the build. Adjust FileSystem::clearExpired method per feedback from initial pull request
issue 6076. avoid GlobIterator globbing to directories which it will subsequently fail to unlink() by appending *.* instead of just * to path in clearByNamespace() and clearByPrefix()