Fix context switching between wd context methods

For example context depended searching like 

     ... .elementByClassName("soria")
            .elementByClassName("mid")
            .end(1)
            .elementByClassName("left")
            .elementByXPath("./..")
            .getAttribute("id").then(function(id) {
                 assert.equal(id, "portal-header");
	     });

in DOM structure:

\<body class="soria"\>
   \<div id="portal-site-container"\>
      \<div id="portal-header"\>
         \<div class="mid"\>xxxx\</div\>
         \<div class="left"\>yyyy\</div\>
       \</div\>
   \</div\>
\</body\>