Fix #706 for RestKit bug where it was loading the same request twice if it failed with timeout when loading request.

 It was failing to properly remove request from "_requests" before calling "loadNextRequest". Took the fix in commit "883d9ac081c978415d7c199cc2f611fa2b2f9379" (https://github.com/sylvainguillope/RestKit/commit/883d9ac081c978415d7c199cc2f611fa2b2f9379).