Make subnet descriptions show address prefixes

Fixes TOOLS-498
Implement DescribeSnapshotAttribute

This is part of TOOLS-494
Implement ResetSnapshotAttribute

Part of TOOLS-494
Make recursive DeleteInstanceProfile try to delete roles

A truly-recursive delete could potentially be catastropic, given that it
would involve recursively-deleting every one of the instance profile's
roles.  Thus, we do not attempt to delete roles recursively here -- if a
role is in use by another resource then deletion will simply fail.

Fixes TOOLS-482
Make BundleInstance attempt to draw creds from config

This commit makes euca-bundle-instance attempt to get access keys and
secret keys from configuration files if they are not supplied at the
command line.  It does not attempt to use the same credentials as the
auth handler that is being used for EC2 because we may be using STS
credentials for the latter.  S3 does not appear to support STS
credentials in POST upload policies.  Moreover, we cannot determine when
STS credentials will expire; if they were to expire while a bundle task
is running the task will fail inexplicably.

Fixes TOOLS-478
Make PostObject policy signature mandatory
Add STS token support to PostObject and bundle upload

Eucalyptus's web console needs to be able to sign S3 POST policies with
STS credentials.  This commit adds an option to the PostObject back end
that allows one to add an x-amz-security-token form field.  It also
makes euca-bundle-and-upload-image pass the token supplied with
--security-token, if any, though to PostObject.

Fixes TOOLS-511
Fix euca-modify-instance-attribute -t call syntax

Fixes TOOLS-510
Update man pages
Merge branch '3.0-maint'