Fix nextPowTwo for 64-bit values under MSVC
Fix nextPowTwo for 64-bit values under MSVC

Summary: A `long` is only 32-bits on MSVC, so this is simply wrong. Shift a `T` left instead.

Reviewed By: yfeldblum

Differential Revision: D3651139

fbshipit-source-id: 3bbfd18ed0c372287c4ec6cbcc543f6f1fcc4139

charsyam/folly,charsyam/folly,rklabs/folly,facebook/folly,facebook/folly,floxard/folly,facebook/folly,floxard/folly,floxard/folly,Orvid/folly,rklabs/folly,Orvid/folly,charsyam/folly,floxard/folly,Orvid/folly,Orvid/folly,rklabs/folly,charsyam/folly,rklabs/folly,facebook/folly,facebook/folly,floxard/folly,rklabs/folly,Orvid/folly