use github maintained gocheck.
magic checksum changes

I'm just changing the checksum to what it expects during my run.

This type of test requires many intimate details of the client
implementaiton, which I don't have. I assume it's the test that's broken
and not the code because the code doesn't seem to have changed, and it's
working anyway. sorry!
tests don't use retrying client.
AddToUserGroup requests
Merge remote-tracking branch 'origin'

Conflicts:
	s3/multi_test.go
Merge pull request #26 from itskripshere/master

AddToUserGroup requests
Merge pull request #27 from mwhooker/master

Fix failing unit tests
aws: style
adds owners argument to Images() as ImagesByOwner()
ec2: Add VirtType parameter to RegisterImage

It's now possible to create instance-store HVM AMIs:

    http://sorcery.smugmug.com/2014/01/29/instance-store-hvm-amis-for-amazon-ec2/

This is controlled by a new optional parameter `VirtType` to
`RegisterImage`, which must be either `paravirtual` or `hvm`.
Merge pull request #31 from LessThanThreeLabs/master

Adds owners argument to Images() as ImagesByOwner()
Add volume tags to DescribeVolumes response
Added ModifyInstanceAttribute API call.
Merge pull request #34 from jmassara/modifyInstance

Add ModifyInstanceAttribute API call.
Merge pull request #32 from grosskur/add-virt-type-to-register-image

ec2: Add VirtType parameter to RegisterImage
Adding tags to the DescribeVolumes response
Merge pull request #35 from jmassara/volTags

Adding tags to the DescribeVolumes response
Include x-amz-security-token in s3 during signing

To quote the documentation:
```
If you are signing your request using temporary security credentials (see Making Requests),
you must include the corresponding security token in your request by adding the
x-amz-security-token header.
```

It wasn't included in headers before, and s3 couldn't be accessed with
the temporary token. Luckily this commit fixes that.
Merge pull request #36 from libc/s3_iam_fix_signing

Include x-amz-security-token in s3 during signing
do not close response until buildError finishes

`s3_test#TestGetNotFound` failed because it's trying to decode hresp.Body, but
the body's already closed. This patch defers `hresp.Body.Close()` until it
finishes building the error.