MRXS huge white borders

[jcupitt at gmail.com]

I thought it was probably best to have cropping to bounds on by
default. I've added a switch called "whole_image" to turn the cropping
off.

https://github.com/jcupitt/libvips/commit/639c22bf5379da524144e40de576d5bd1907d57a

This changes default behaviour and therefore breaks compatibility,
which is very bad, but I hope it won't be too bad for to many people,
and longer term the simplicity is a good benefit. Complain now if you
think this is a serious problem!

Disable the cropping like this:

vips dzsave CMU-1.mrxs[whole_image] my_pyramid

The change will be in the next stable version, due in a few days.

John