FileServer
FileServer

Summary: Based on new FileRegion interface

Test Plan: ran it, streamed lots of files. I have found an obscure way to break it but I don't think it's a FileRegion issue, rather a pipeline/bootstrap issue. Still digging

Reviewed By: hans@fb.com

Subscribers: fugalh, folly-diffs@, jsedgwick, yfeldblum, chalfant

FB internal diff: D2088094

Signature: t1:2088094:1432758904:0f1e5765dbedea5ddbe047db50e7b632cfb0c053

rklabs/wangle,Orvid/wangle,jamperry/wangle,raphaelamorim/wangle,rklabs/wangle,mzhaom/wangle,Dalzhim/wangle,Dalzhim/wangle,orian/wangle,AresTao/wangle,Orvid/wangle,facebook/wangle,raphaelamorim/wangle,jamperry/wangle,mzhaom/wangle,facebook/wangle,orian/wangle,AresTao/wangle,facebook/wangle