fix input sizing when placeholder is set. fixes #192

select2.js

@@ -1550,7 +1550,7 @@
             if (placeholder !== undefined  && this.getVal().length === 0 && this.search.hasClass("select2-focused") === false) {
                 this.search.val(placeholder).addClass("select2-default");
                 // stretch the search box to full width of the container so as much of the placeholder is visible as possible
-                this.search.width(this.getContainerWidth());
+                this.search.width(this.container.width());
             } else {
                 // we set this to " " instead of "" and later clear it on focus() because there is a firefox bug
                 // that does not properly render the caret when the field starts out blank