Add NODE_BLOOM service bit and bump protocol version

Lets nodes advertise that they offer bloom filter support explicitly.
The protocol version bump allows SPV nodes to assume that NODE_BLOOM is
set if NODE_NETWORK is set for pre-170004 nodes.

Also adds an option to turn bloom filter support off for nodes which
advertise a version number >= 170004. Nodes attempting to use bloom
filters on such protocol versions are banned, and a later upgade
should drop nodes of an older version which attempt to use bloom
filters.

Much code stolen from Peter Todd.

Zcash: Implements Zcash equivalent of BIP 111; deploys with Overwinter

src/protocol.h

@@ -71,6 +71,10 @@ enum {
     // set by all Bitcoin Core nodes, and is unset by SPV clients or other peers that just want
     // network services but don't provide them.
     NODE_NETWORK = (1 << 0),
+    // NODE_BLOOM means the node is capable and willing to handle bloom-filtered connections.
+    // Zcash nodes used to support this by default, without advertising this bit,
+    // but no longer do as of protocol version 170004 (= NO_BLOOM_VERSION)
+    NODE_BLOOM = (1 << 2),
 
     // Bits 24-31 are reserved for temporary experiments. Just pick a bit that
     // isn't getting used, or one not being used much, and notify the