Implements the Storage interface for Google Storage.
A GoogleStorage instance stores blobs in a single Google Storage bucket, with
each blob keyed by its blobref.  

Testing:

gsapi_test.go contains integration tests which run against Google Storage.
In order to run these tests properly, you will need to:

1.  Set up google storage.  See:
	http://code.google.com/apis/storage/docs/signup.html

2.  Upload the contents of the testdata dir to a google storage bucket.  Note
	that all these files begin with 'test-': such files will be ignored when 
	the bucket is used as blobserver storage.

3.  Create the config file '~/.camli/gstestconfig.json'.  The file should look
	something like this:

	{
			"auth": {
				"client_id": "your client id",
				"client_secret": "your client secret",
				"refresh_token": "a refresh token"
			},
			"bucket": "bucket.example.com"
	}

	You can use camgsinit to help obtain the auth config object.