The main feature for this version upgrade is the use of the instruction
emulator (IEM) to speed up execution and less often the slow recompiler.
issue #2059
Add option to load the initial overlay*.vdi from disk, but keep the changes
in a ram_fs.
Used with AHCI model for vbox_auto_win7. Currently we have no way to tell
rump_fs to unmount and write back data to disk before resetting the machine.
