#262 setImageInterlaceScheme doesn't make image progressive

[Isius]

Attempts to use the PHP wrapper GMagick to set the interlace scheme to interlaced results in no change in the image. The problem was first reported to the PHP GMagick team at https://bugs.php.net/bug.php?id=66444 However, in an email they replied "Does not seem like a gmagick issue: https://github.com/vitoc/gmagick/blob/master/gmagick_methods.c#L2156" and that I should report the problem here.

Note that gm convert in.jpg -interlace Line out.jpg does in fact produce an interlaced image as expected.

[Bob Friesenhahn]

The problem is that MagickSetInterlaceScheme() should be used to set the interlace scheme used when writing the image. No source code changes in GraphicsMagick are required. Sorry that this interface is so confusing. I see that the documentation should be improved so I will improve the descriptions of the two functions.