Add 'virt-rescue' command.

This command runs a "rescue appliance" against a virtual machine
or disk image.  This is useful for making ad-hoc interactive
changes to virtual machines.

  $ virt-rescue --ro /dev/vg_trick/F11x64

  Welcome to virt-rescue, the libguestfs rescue shell.

  Note: The contents of / are the rescue appliance.
  You have to mount the guest's partitions under /sysroot
  before you will be able to examine them.

  bash: cannot set terminal process group (-1): Inappropriate ioctl for device
  bash: no job control in this shell
  ><rescue> mount /dev/vg_f11x64/lv_root /sysroot
  EXT4-fs (dm-0): barriers enabled
  kjournald2 starting: pid 269, dev dm-0:8, commit interval 5 seconds
  EXT4-fs (dm-0): internal journal on dm-0:8
  EXT4-fs (dm-0): delayed allocation enabled
  EXT4-fs: file extents enabled
  EXT4-fs: mballoc enabled
  EXT4-fs (dm-0): mounted filesystem with ordered data mode
  ><rescue> ls /sysroot/
  bin   dev  home  lib64       media  opt   root  selinux  sys  usr
  boot  etc  lib   lost+found  mnt    proc  sbin  srv      tmp  var
  ><rescue> exit

1 files changed, 16 insertions, 0 deletions

diff --git a/TODO b/TODO
index 12b1ce68..2833d461 100644
--- a/TODO
+++ b/TODO
@@ -264,3 +264,19 @@ quickly, eg:
   load ext2
 
 Maybe it's better to create these on the fly?
+
+virt-rescue pty
+---------------
+
+See:
+http://search.cpan.org/~rgiersig/IO-Tty-1.08/Pty.pm
+http://www.perlmonks.org/index.pl?node_id=582185
+
+Note that pty requires cooperation inside the C code too (there are
+two sides to a pty, and one has to be handled after the fork).
+
+virt-rescue TERM
+----------------
+
+Pass TERM from the library, through the kernel command line, to the
+init script.