Tests: Fix flaky dump test "Circular reference with arrays"

There were two issues here:

* The test relied on non-default maxDepth of null or > 10 since
  its example involves recurion 10 levels deep, and the default
  maxDepth is 5.

* There is a bug in `QUnit.dump.parse()` where, if the input value
  cannot be mapped to a formatter function, it returns a function
  instead of a string.

  This bug was introduced nearly ten years ago in commit 818b2be,
  where `error` was replaced with a function that had a different
  purpose than what was there before, and this one use of it as
  fallback was not updated.

  Unfortunately, I am unable to say what value causes this to happen.
  I can consistently reproduce the issue in Safari 9.1 via BrowserStack,
  but only if I don't open the console, don't run a subset of the test,
  and don't modify any of the surrounding code. I have tried dozens
  upon dozens of clever ways to store values during the parse() function
  call in temporary variables and alert() them but as soon as I tried
  to capture anything that would help, the bug would stop happening.

  I can only conclude that there must be some kind of memory or JIT
  corruption in the JavaScript engine of Safari 9.1 that has some
  extremely specific conditions attached to it. Conditions that we
  did not meet before the last few commits, and are meeting now.

```
[OS X El Capitan, Safari 9.1] Error: "Circular reference with arrays" failed
Died on test #1 @http://localhost:8899/test/main/dump.js:279:11:
expected.indexOf is not a function.
(In 'expected.indexOf("[object Array]")', 'expected.indexOf' is undefined)
```

src/dump.js

@@ -104,7 +104,10 @@ export default ( function() {
 				stack.pop();
 				return res;
 			}
-			return ( parserType === "string" ) ? parser : this.parsers.error;
+			if ( parserType === "string" ) {
+				return parser;
+			}
+			return "[ERROR: Missing QUnit.dump formatter for type " + objType + "]";
 		},
 		typeOf: function( obj ) {
 			let type;
@@ -180,6 +183,9 @@ export default ( function() {
 			error: function( error ) {
 				return "Error(\"" + error.message + "\")";
 			},
+
+			// This has been unused since QUnit 1.0.0.
+			// @todo Deprecate and remove.
 			unknown: "[Unknown]",
 			"null": "null",
 			"undefined": "undefined",

test/main/dump.js

@@ -3,6 +3,8 @@
 
 QUnit.module( "dump", {
 	afterEach: function() {
+
+		// Restore default
 		QUnit.dump.maxDepth = null;
 	}
 } );
@@ -239,6 +241,8 @@ function chainwrap( depth, first, prev ) {
 QUnit.test( "Check dump recursion", function( assert ) {
 	var noref, nodump, selfref, selfdump, parentref, parentdump, circref, circdump;
 
+	// QUnit.dump.maxDepth = 20;
+
 	noref = chainwrap( 0 );
 	nodump = QUnit.dump.parse( noref );
 	assert.equal( nodump, "{\n  \"first\": true,\n  \"wrap\": undefined\n}" );
@@ -263,6 +267,8 @@ QUnit.test( "Check dump recursion", function( assert ) {
 QUnit.test( "Check equal/deepEqual recursion", function( assert ) {
 	var noRecursion, selfref, circref;
 
+	// QUnit.dump.maxDepth = 20;
+
 	noRecursion = chainwrap( 0 );
 	assert.equal( noRecursion, noRecursion, "I should be equal to me." );
 	assert.deepEqual( noRecursion, noRecursion, "... and so in depth." );