Added slightly better error handling in getFeed
Added slightly better error handling in getFeed

One version of node had come cert problem with talking to google servers
and the error message about it was useless. Passing though the error
message from the request was helpful to figuring that out (and probably
the right thing to do).

AfterShip/node-google-spreadsheets,arve0/node-google-spreadsheets,samcday/node-google-spreadsheets