mksquashfs can read uid/gid/file type from fakeroot(1) database

[asheplyakov]

With this patch I can easily pack chroots built in a fakeroot environment without running mksquashfs under fakeroot. Instead I can use -fakerootdb .fakedata to get ownership/permissions/device nodes right.

It's possible to convert fakeroot database into mksquashfs' pseudo files definitions but using the fakeroot database directly is more efficient (fakeroot uses device/inode number to identify the object) and requires less code.