trace: split code out of vfs_optimizer (was getting too large)
vfs_mount: expose API to unmount all (needed to be able to delete
archives after building)
vfs_optimizer: safely handle empty connection/node lists;
refactored+documented
vfs_tree: eliminate 'file in root dir' warning (can happen easily
enough)
rest: fixes/minor tweaks
This was SVN commit r3610.
