function addFileFilter(name, cb) {
		fileFilters[name] = cb;
	}
Registers a filter that will be executed for each file added to the queue.
If callback returns false, file will not be added.

Callback receives two arguments: a value for the filter as it was specified in settings.filters
and a file to be filtered. Callback is executed in the context of uploader instance.

@method addFileFilter
@static
@param {String} name Name of the filter by which it can be referenced in settings.filters
@param {String} cb Callback - the actual routine that every added file must pass