Provide CLI options to disable aspects of soft-fork.

Soft-fork will remain default behaviour, but you can now disable
either the whole mechanism (you'll lose money if you mine with this
when the majority network doesn't) or just vote against it but
otherwise go with the flow.

ethcore/res/ethereum/frontier.json

@@ -9,7 +9,8 @@
 				"durationLimit": "0x0d",
 				"blockReward": "0x4563918244F40000",
 				"registrar" : "0xc6d9d2cd449a754c494264e1809c50e34d64562b",
-				"frontierCompatibilityModeLimit": "0x118c30"
+				"frontierCompatibilityModeLimit": "0x118c30",
+				"daoRescueSoftFork": false
 			}
 		}
 	},