add unregister_target to CommManagers

IPython/html/static/services/kernels/js/comm.js

@@ -45,6 +45,11 b' var IPython = (function (IPython) {'
         this.targets[target_name] = f;
     };
     
+    CommManager.prototype.unregister_target = function (target_name, f) {
+        // Unregister a target function for a given target name
+        delete this.targets[target_name];
+    };
+
     CommManager.prototype.register_comm = function (comm) {
         // Register a comm in the mapping
         this.comms[comm.comm_id] = comm;

IPython/kernel/comm/manager.py

@@ -89,6 +89,10 b' class CommManager(LoggingConfigurable):'
         
         self.targets[target_name] = f
     
+    def unregister_target(self, target_name, f):
+        """Unregister a callable registered with register_target"""
+        return self.targets.pop(target_name);
+
     def register_comm(self, comm):
         """Register a new comm"""
         comm_id = comm.comm_id