Add Message#cmd_sym as a convenience method

lib/btc_wire_proto.rb

@@ -398,6 +398,11 @@ module BtcWireProto
     uint32 :payload_len
     uint32 :checksum, :onlyif => :has_checksum?
     
+    def cmd_sym
+      c = command.strip
+      c == "" ? nil : c.to_sym
+    end
+    
     protected
     
     # version and verack messages don't have a checksum. The rest do.
@@ -421,6 +426,10 @@ module BtcWireProto
 
     message_hdr :header
     
+    def cmd_sym
+      header ? header.cmd_sym : nil
+    end
+    
     choice :payload, :selection => :payload_choice do
       version         "version"
       addr_pre31402   "addr_pre31402"