Added '0store copy' command. This copies a possibly-untrusted directory

Added '0store copy' command. This copies a possibly-untrusted directory

structure into your cache (by default), checking that it matches the requested
digest. This is useful if you notice that a user you don't fully trust already
has a program you were about to download - you can safely get a copy from them.

A little more work may be needed to make this completely robust. When ready,
the injector can be made to check for suitable directories to copy
automatically before starting a download.

This may also be useful in the long-planned setuid script to copy downloads
by users into the shared system directory (since it will only copy correctly
named directories).

git-svn-id: file:///home/talex/Backups/sf.net/Subversion/zero-install/trunk/0launch@1016 9f8c893c-44ee-0310-b757-c8ca8341c71e