Added support for custom object formatters

Custom object formatters allow users to customize how an object is
stringified in matcher failure messages. This can already be done by
adding a `jasmineToString` method to the objects in question. But
it's not always desirable or possible to do that, particularly when
objects of a given "type" do not inherit from a specific prototype.
For instance, suppose a web service returns a list of foos that are
deserialized from JSON, e.g.:

   { fooId: 42, /* more properties */ }

The only way to define `jasmineToString` on those is by writing code to
add it to each instance at runtime. But a custom object formatter can
recognize that the object it's looking at is a foo and format it
accordingly:

   jasmine.addCustomObjectFormatter(function(obj) {
      if (typeof obj.fooId !== 'number') {
            return undefined;
        }

        return '[Foo with ID ' + obj.fooId + ']';
    });

Unlike `jasmineToString`, custom object formatters are scoped to a
particular spec or suite and don't require any changes to the code
under test.

spec/core/matchers/toBeSpec.js

@@ -59,4 +59,16 @@ describe("toBe", function() {
     expect(result.pass).toBe(false);
     expect(result.message).toBe("Expected Object({ foo: 'bar' }) to be Object({ foo: 'bar' }). Tip: To check for deep equality, use .toEqual() instead of .toBe().")
   });
+
+  it("works with custom object formatters when expected is an object", function() {
+    var formatter = function(x) { return '<' + x.foo + '>'; },
+      prettyPrinter = jasmineUnderTest.makePrettyPrinter([formatter]),
+      util = new jasmineUnderTest.MatchersUtil({pp: prettyPrinter}),
+      matcher = jasmineUnderTest.matchers.toBe(util),
+      result;
+
+    result = matcher.compare({foo: "bar"}, {foo: "bar"});
+    expect(result.pass).toBe(false);
+    expect(result.message).toBe("Expected <bar> to be <bar>. Tip: To check for deep equality, use .toEqual() instead of .toBe().")
+  });
 });