Fix Tab while there's a selection not Tabbing away

By "Tabbing away" I mean that if something is focused, and you hit Tab,
you expect focus to jump to the next thing in tab order.

Normally that happens in MathQuill editable fields whenever the cursor
is in the root block/at the top level. But, a bug was intro'd by mathquill#294
and reported in mathquill#413 that if there's a selection, then even if you're in
the root block, when you hit Tab, focus wouldn't actually jump to the
next thing. Instead, the math field would look blurred but the hidden
textarea would "steal back" focus, and you could type in the seemingly-
blurred MathQuill editable field, see GIF: https://git.io/v2UGL
(The "Show Textareas" button in the top-right corner of test/visual.html
 was used to show the normally hidden textareas.)

Note that this bug also affected API clients who in a handler like
`upOutOf` that's called synchronously on `keydown`, blur the textarea
(for example, by focusing something above the math field), which is
exactly what mathquill#355 was supposed to fix. Turns out the test case in mathquill#355
isn't representative, the fix only seemed to work because for
jQuery ≤1.8.3 (our tests use 1.7.2), when you call jQuery's `.blur()`
method, the `blur` event handlers are called while the hidden textarea
is still focused, so the `textarea[0].select()` doesn't "steal back"
focus. However, when Tabbing away, or when the `upOutOf` or whatever
handler focuses something else, or when you call jQuery ≥1.9.0's
`.blur()` method, or (luckily for our tests) when you call the DOM's
"native" `.blur()` method, the hidden textarea is already blurred, so
the `textarea[0].select()` "steals back" focus, hence bug and fix.

Isolated test case demonstrating this for jQuery 1.8.3 vs jQuery 1.9.0
vs the DOM's "native" `.blur()` method:
http://jsbin.com/kepaxo/5/edit?console,output

src/services/saneKeyboardEvents.util.js

@@ -109,7 +109,7 @@ var saneKeyboardEvents = (function() {
       clearTimeout(timeoutId);
       timeoutId = setTimeout(checker);
     }
-    target.bind('keydown keypress input keyup focusout paste', function() { checkTextarea(); });
+    target.bind('keydown keypress input keyup focusout paste', function(e) { checkTextarea(e); });
 
 
     // -*- public methods -*- //
@@ -148,8 +148,10 @@ var saneKeyboardEvents = (function() {
       keydown = e;
       keypress = null;
 
-      if (shouldBeSelected) checkTextareaFor(function() {
-        if (textarea[0].select) textarea[0].select(); // re-select textarea in case it's an unrecognized
+      if (shouldBeSelected) checkTextareaFor(function(e) {
+        if (!(e && e.type === 'focusout') && textarea[0].select) {
+          textarea[0].select(); // re-select textarea in case it's an unrecognized
+        }
         checkTextarea = noop; // key that clears the selection, then never
         clearTimeout(timeoutId); // again, 'cos next thing might be blur
       });

test/unit/focusBlur.test.js

@@ -0,0 +1,53 @@
+suite('focusBlur', function() {
+  suite('handlers can shift focus away', function() {
+    var mq, mq2, wasUpOutOfCalled;
+    setup(function() {
+      mq = MQ.MathField($('<span></span>').appendTo('#mock')[0], {
+        handlers: {
+          upOutOf: function() {
+            wasUpOutOfCalled = true;
+            mq2.focus();
+          }
+        }
+      });
+      mq2 = MQ.MathField($('<span></span>').appendTo('#mock')[0]);
+      wasUpOutOfCalled = false;
+    });
+    teardown(function() {
+      $(mq.el()).add(mq2.el()).remove();
+    });
+
+    function triggerUpOutOf(mq) {
+      $(mq.el()).find('textarea').trigger(jQuery.Event('keydown', { which: 38 }));
+      assert.ok(wasUpOutOfCalled);
+    }
+    function assertHasFocus(mq, name) {
+      assert.ok($(mq.el()).find('textarea').is(':focus'), name + ' has focus');
+    }
+
+    test('normally', function() {
+      mq.focus();
+      assertHasFocus(mq, 'mq');
+
+      triggerUpOutOf(mq);
+      assertHasFocus(mq2, 'mq2');
+    });
+
+    test('even if there\'s a selection', function(done) {
+      mq.focus();
+      assertHasFocus(mq, 'mq');
+
+      mq.typedText('asdf');
+      assert.equal(mq.latex(), 'asdf');
+
+      mq.keystroke('Shift-Left');
+      setTimeout(function() {
+        assert.equal($(mq.el()).find('textarea').val(), 'f');
+
+        triggerUpOutOf(mq);
+        assertHasFocus(mq2, 'mq2');
+        done();
+      });
+    });
+  });
+});

test/unit/saneKeyboardEvents.test.js

@@ -166,7 +166,7 @@ suite('key', function() {
         var shim = saneKeyboardEvents(el, {
           keystroke: function(key) {
             assert.equal(key, 'Left');
-            el.blur();
+            el[0].blur();
           }
         });