Bug 18505

VFS_START is not called after VFS_MOUNT in vfs_mountroot_try (vfs_conf.c).
This is contrary to VFS_START's intention and documentation. The deed
only goes unpunished because no filesystem currently does anything on
VFS_START except MFS, but it's only a matter of time before some might
try something. MFS grabs the calling process and turns it into a workhorse
on VFS_START, but MFS won't mount as root so it's okay (and correct) 
to call VFS_START there.

Fix: Two choices:
1) Document VFS_START as a dirty hack made especially for MFS which no
other filesystems should ever use or rely on;
2) (preferrable IMHO) apply the patch below. It also fixes a typo in
the comment for MFS code which stops it from mounting as root.