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-70011 nodes.

Also adds an option to turn bloom filter support off for nodes which
advertise a version number >= 70011. 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.

Implements BIP 111

src/protocol.h

@@ -75,6 +75,10 @@ enum {
     // Bitcoin Core does not support this but a patch set called Bitcoin XT does.
     // See BIP 64 for details on how this is implemented.
     NODE_GETUTXO = (1 << 1),
+    // NODE_BLOOM means the node is capable and willing to handle bloom-filtered connections.
+    // Bitcoin Core nodes used to support this by default, without advertising this bit,
+    // but no longer do as of protocol version 70011 (= 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