Decoding at the precinct level

[boxerab]

It would be useful to be able to decode a sub-window inside a tile. This is feedback I got
from the GDAL news group.

This would involve decoding all precincts that overlap with the sub-window,
including code blocks adjacent to precincts that share a boundary with the
window. Then, inverse MQ on all blocks, dequantize, sparse inverse DWT on
only the sub window, then inverse MCT on only the sub window.