Improve the Amazon EC2 script.

It now has getopts support, a help message, specifies regions
correctly to avoid manifest errors, and is less verbose.  The
need for sudo will disappear shortly when I integrate some code
from @djs55 that creates the block device from OCaml directly
without needing a loop device.
sync CHANGES
Merge pull request #237 from avsm/ec2-script

Improvements to EC2 deployment script
Augment STACKV4 with an IPV4 module in addition to TCPV4 and UDPV4.

This should really have been in the original commit, since without
the IPV4 module exposed, it's not possible to manipulate the IP
configuration of the stack from an external API.

This requires the associated commit in mirage/mirage-tcpip#50
Merge branch 'master' of github.com:mirage/mirage
update CHANGES
Regenerate with OASIS 0.4.4 (which adds natdynlink support)