The standard PNG reader plug-in provides incorrect information to various
event listener methods:

1) The percentageDone argument to IIOReadProgressListener.imageProgress
   restarts at 0% for each pass instead of increasing monotonically
2) IIOReadUpdateListener.imageUpdate was not called.

daniel.rice@Eng 2000-12-07

The GIF reader also provides an incorrect value to processPassStarted if
the file is non-interlaced (it claims the Y step is 8 when in fact it is
1).