Revert "Revert passing content body to http request (#619)" (#621)

This reverts commit f804d79. One bug
was wrongly understood and led to a wrong revert.

api.go

@@ -588,7 +588,7 @@ func (c Client) newRequest(method string, metadata requestMetadata) (req *http.R
 	}
 
 	// Initialize a new HTTP request for the method.
-	req, err = http.NewRequest(method, targetURL.String(), nil)
+	req, err = http.NewRequest(method, targetURL.String(), metadata.contentBody)
 	if err != nil {
 		return nil, err
 	}
@@ -608,11 +608,6 @@ func (c Client) newRequest(method string, metadata requestMetadata) (req *http.R
 		return req, nil
 	}
 
-	// Set content body if available.
-	if metadata.contentBody != nil {
-		req.Body = ioutil.NopCloser(metadata.contentBody)
-	}
-
 	// FIXME: Enable this when Google Cloud Storage properly supports 100-continue.
 	// Skip setting 'expect' header for Google Cloud Storage, there
 	// are some known issues - https://github.com/restic/restic/issues/520