These two patches are related to:
https://bugzilla.redhat.com/show_bug.cgi?id=730909
The first removes the obvious problem of attempting to feed qemu
invalid options. The second makes it possible to specify a different
policy for read errors and write errors. 1/2 is written such that 2/2
will apply with minimal rewriting of existing code (that's why the
qemu_command.c part may seem a bit obtuse at first).