Backported from X.org:

 commit acda790e430b2a18c7c35379f6e538f3d01ff221
 Author: Keith Packard <keithp@keithp.com>
 Date:   Fri Mar 14 13:46:30 2008 -0700

    [render] Split out filter finding from filter setting.

    To prepare for RandR using filters in transforms, split out
    code paths so that the RandR code can validate the filter name and
    parameters during the transform set operation so that use of the filter
    later will not have unreportable errors.

 Backport to nx-libs: Mike Gabriel <mike.gabriel@das-netzwerkteam.de>