Fix #13076. Speed up $() with strings, part of gh-1089.

AUTHORS.txt

@@ -156,4 +156,4 @@ Matthias Jäggli <matthias.jaeggli@gmail.com>
 Yiming He <yiminghe@gmail.com>
 Devin Cooper <cooper.semantics@gmail.com>
 Bennett Sorbo <bsorbo@gmail.com>
- 
\ No newline at end of file
+Sebastian Burkhard <sebi.burkhard@gmail.com>

src/core.js

@@ -96,8 +96,8 @@ jQuery.fn = jQuery.prototype = {
 			return this;
 		}
 
-		// HANDLE: $(DOMElement)
-		if ( selector.nodeType ) {
+		// HANDLE: $(DOMElement); check first that selector is not a primitive
+		if ( typeof selector === "object" && selector.nodeType ) {
 			this.context = this[0] = selector;
 			this.length = 1;
 			return this;