fix xccmd to find proper target. Previously xccmd command just calls the action with target "nil" which eventually handled by responder chain.
Since some actions in menu has a concrete target and we must specify it when invoking now we find the action from menu and specify the target as well.

Conflicts:

	XVim/XVimExCommand.m
Merge branch 'master' of github.com:JugglerShu/XVim

* 'master' of github.com:JugglerShu/XVim:
  Update README.md
  amend comment typo
  fix bug 'dw' and 'dW' issue #346