Merge pull request bitcoin#457 from laanwj/2016_10_bip144_add_constants

bip-0144: Add enum values for MSG_WITNESS_{BLOCK,TX}, MSG_FILTERED_WITNESS_BLOCK

bip-0144.mediawiki

@@ -103,9 +103,9 @@ and therefore, they have witness hash equal to normal hash.)
 <img src=bip-0144/witnesstx.png></img>
 
 === Relay ===
-New inv types MSG_WITNESS_TX and MSG_WITNESS_BLOCK are added, only
+New inv types MSG_WITNESS_TX (0x40000001, or (1<<30)+MSG_TX) and MSG_WITNESS_BLOCK (0x40000002, or (1<<30)+MSG_BLOCK) are added, only
 for use in getdata. Inventory messages themselves still use just MSG_TX and MSG_BLOCK,
-similar to MSG_FILTERED_BLOCK.
+similar to MSG_FILTERED_BLOCK. A further inv type MSG_FILTERED_WITNESS_BLOCK (0x40000003, or (1<<30)+MSG_FILTERED_BLOCK) is reserved for future use.
 
 * '''Rationale for not advertizing witnessness in invs''': we don't always use invs anymore (with 'sendheaders' BIP 130), plus it's not useful: implicitly, every transaction and block have a witness, old ones just have empty ones.