Fix nickname_commands loading that got lost along the way.

The for loop that adds nickname_commands to the func.rules
got lost along the way to prevent duplicate regexp rules for
a given func.

sopel/loader.py

@@ -169,6 +169,11 @@ def clean_callable(func, config):
                 # See issue 1056
                 # TODO: Maybe func.rule should be a set() instead?
                 func.rule.append(regexp)
+        for command in getattr(func, 'nickname_commands', []):
+            regexp = get_nickname_command_regexp(nick, command, alias_nicks)
+            if regexp not in func.rule:
+                # See for-loop immediately above this.
+                func.rule.append(regexp)
         if hasattr(func, 'example'):
             example = func.example[0]["example"]
             example = example.replace('$nickname', nick)