Try to move the caret within the viewport on entering Caret or Find mode. Closes issue #170.

common/content/modes.js

@@ -93,6 +93,8 @@ var Modes = Module("modes", {
                     modes.pop();
                 else if (!stack.pop && !this.pref)
                     this.pref = true;
+                if (!stack.pop)
+                    buffer.resetCaret();
             },
 
             leave: function (stack) {