accessPolicy: Implement Put, Get, Delete access policy.

This patch implements Get,Put,Delete bucket policies

Supporting - http://docs.aws.amazon.com/AmazonS3/latest/dev/access-policy-language-overview.html

Currently supports following actions.

   "*":                             true,
   "s3:*":                          true,
   "s3:GetObject":                  true,
   "s3:ListBucket":                 true,
   "s3:PutObject":                  true,
   "s3:CreateBucket":               true,
   "s3:GetBucketLocation":          true,
   "s3:DeleteBucket":               true,
   "s3:DeleteObject":               true,
   "s3:AbortMultipartUpload":       true,
   "s3:ListBucketMultipartUploads": true,
   "s3:ListMultipartUploadParts":   true,

following conditions for "StringEquals" and "StringNotEquals"

   "s3:prefix", "s3:max-keys"

generic-handlers.go

@@ -280,7 +280,7 @@ func ignoreNotImplementedObjectResources(req *http.Request) bool {
 
 // List of not implemented bucket queries
 var notimplementedBucketResourceNames = map[string]bool{
-	"policy":         true,
+	"acl":            true,
 	"cors":           true,
 	"lifecycle":      true,
 	"logging":        true,