The file upload function has incorrect permission check

[Nicklas Nordborg]

It checks for WRITE permission on the directory but according to the BASE documentation and the implementation in the BASE core USE permission should be enough to be able to create files in a directory.

This only affects file upload from the web client GUI. Creating a file reference to an URL works, and plug-ins can also create files in the directory. The workaround is to give the user WRITE permission to the directory.

[Nicklas Nordborg]

(In [7242]) Fixes #2046: The file upload function has incorrect permission check