Pict improvements

[andrews05]

There’s a lot of changes in here, I’ll try to outline the key points:

• Recognise (and ignore) more opcodes
• Always ignore alpha
• Adhere to the destination rect in direct bits, while also making sure not to overflow the surface bounds
• Correct determining when to use packbits, for both decoding and encoding
• Support all pack types, including 1 and 2

Together these fix a number of weird picts and edge cases.

[andrews05]

Updated with proper support for pack types 1 & 2. This finally fixes some decoding the polycon button images that previously appeared green.