(documented) The stream_tell() method cannot be overridden with a wrapper

(documented) The `stream_tell()` method cannot be overridden with a wrapper

This sadness was fixed by changing the documentation to describe the actual way to trigger php streamwrapper.stream-tell - php function.fseek.

Previously, PHP's stream wrapper system documentation indicated that stream_tell was invoked by ftell, but this was not the case.