Fix a regression introduced by cba36ce

Request.prototype.init() should not clear self.method if it is already
set.  This is relevant when retrying requests with proper authentication
(the retries are handled similarly to redirects, but should keep the
same request method).

index.js

@@ -126,7 +126,7 @@ Request.prototype.init = function (options) {
   var self = this
   if (!options) options = {}
 
-  self.method = options.method || 'GET'
+  if (!self.method) self.method = options.method || 'GET'
 
   debug(options)
   if (!self.pool && self.pool !== false) self.pool = globalPool