Improved icns support

[al45tair]

Adds support for PNG-encoded .icns files with of up to 512x512 (plus retina, so 1024x1024 at most).

[al45tair]

PIL also needs support for JPEG 2000 .icns files (yes, they’re in use; an example is EyeTV’s icon), but that will have to wait until #547 has been merged.

[wiredfool]

Looks pretty good to me. I know we didn't have any tests on this before, but I'd like to get some in before merging.

[al45tair]

@wiredfool As before, I’m happy to add some tests. Does Pillow have its own icon? If it does, the test cases should probably use an .icns file of that. If not, maybe it should have? Thoughts?

[wiredfool]

There's no icon, and as far as I can tell no branding to turn into an icon. I'm open to improvements there. @aclark4life?

[aclark4life]

Yes! Love the idea of adding icon support

[wiredfool]

I was meaning an icon for Pillow. Branding. Publicity. Fame. Fortune!. or at least a beer. or something.

[aclark4life]

Ah! Don't care. Sure, why not.

[aclark4life]

@al45tair Can you address @wiredfool 's conditional import comment so we can merge this? Thanks

[wiredfool]

And tests.

[wiredfool]

Not to be impatient about them or anything.

[aclark4life]

Well, the 2.4.0 deadline is coming…

[al45tair]

@aclark4life The conditional import comment refers to JPEG 2000 support, which (intentionally) isn't included in this particular iteration of the IcnsFilePlugin code, so I don’t think that’s a blocker for merging, unless you also want me to do the same for the use of the PNG plugin?

@wiredfool I'll knock together some simple tests today.

[al45tair]

@aclark4life @wiredfool OK, tests added, and a pre-existing bug affecting Python 3 fixed. Also, I don't know what you think about the icon in Images/pillow.icns? The image files on which it’s based are both mine (I took the photos in question), so there aren’t any copyright issues.

[al45tair]

@aclark4life @wiredfool Since the JPEG 2000 support was merged, I’ve merged in my JPEG 2000 .icns support and added another test image. The JPEG 2000 code is conditionally imported, as requested.