- added PHP utility function to check for file name validity
- fixes issue where a user can create a file called ".." from the files UI
- added extra checks to make sure newfile.php and newfolder.php also
check for invalid characters
Whent trying to upload/rename/create files in a folder that was removed
or rename, the correct error message is now shown.
In the case of upload of multiple files, the upload is cancelled.
This situation can happen if the target folder was renamed or removed
from another browser window or client.