[feature request] Partition table wrapper for single-filesystem images

Suppose you have a single filesystem image. It would be nice if QEMU could generate a virtual partition table for it and make it available to the guest as a partitioned disk. Otherwise you have to use workarounds like this: wiki.archlinux.org/index.php/QEMU#Simulate_virtual_disk_with_MBR_using_linear_RAID

It should be relatively easy to do on top of existing vvfat code.