Not able to provide TIFF image format reader. Qt's is always used.

I would like to provide my own TIFF reader, but the system is using the native version.  I cannot find a way to force Qt to use my TIFF image reader.  My plugin is called for png files.

Keys are registered in plugin and canRead returns true.

There are several ways to address this::

1) Provide a way to remove image reader plugins

2) Scan external plugins first and use first matching