rpcserver: Improve JSON-RPC compatibility
rpcserver: Improve JSON-RPC compatibility

In order to avoid compatibility issues with software relying on 
Core's behavior, terminate HTTP POST JSON-RPC responses with a newline.
dajohi/btcd,cqswxj2013/btcd,davecgh/btcd,dajohi/btcd,jrick/dcrd,adiabat/btcd,Roasbeef/btcd,aakselrod/btcd,wallclockbuilder/btcd,ppcsuite/ppcd,decred/dcrd,Stash-Crypto/btcd,btcsuite/btcd,ltcsuite/ltcd,jongillham/btcd,adiabat/btcd,btcsuite/btcd,aakselrod/btcd,jongillham/btcd,tb00/btcd,wallclockbuilder/btcd,dajohi/btcd,cqswxj2013/btcd,tb00/btcd,Roasbeef/btcd,stevenroose/btcd,Stash-Crypto/btcd,ppcsuite/ppcd,decred/dcrd,ltcsuite/ltcd,stevenroose/btcd,jrick/dcrd,davecgh/btcd