This patch changes the release script in the following ways:
- A staging directory is always used to avoid oversized images;
- As a consequence, the zero-filling is removed so no more "out of
space" errors should be printed to the console;
- The root and usr partition sizes are computed so less space should be
wasted (the root partition gets extra 1MB zones and 64 inodes for
run-time though and hardlinks/holes make the used space slightly less
than expected); USRMB (and the new ROOTMB) are now used to enforce
a minimum size rather than set the size;
- TMPDISK1-3 are renamed to more meaningful names (and TMPDISK2 is
dropped because a separate tmp directory is no longer needed);
- The ramdisks are truncated at the end to save memory (not sure
whether it is actually released though).