Ignore part checksums in CompleteMultipartUpload

The intent of these are to correlate with the headers from previous
UploadPart requests.  S3Proxy ignores these elements for now since
none of the storage backends support them.  References #656.

src/main/java/org/gaul/s3proxy/CompleteMultipartUploadRequest.java

@@ -32,6 +32,16 @@ final class CompleteMultipartUploadRequest {
         int partNumber;
         @JacksonXmlProperty(localName = "ETag")
         String eTag;
+
+        // TODO: unsupported checksums
+        @JacksonXmlProperty(localName = "ChecksumCRC32")
+        String checksumCRC32;
+        @JacksonXmlProperty(localName = "ChecksumCRC32C")
+        String checksumCRC32C;
+        @JacksonXmlProperty(localName = "ChecksumSHA1")
+        String checksumSHA1;
+        @JacksonXmlProperty(localName = "ChecksumSHA256")
+        String checksumSHA256;
     }
 }
 // CHECKSTYLE:ON