Revert "Use default failure message for toBeNaN"

Forgot that NaN has special casing that it needs a custom error message
for

This reverts commit b6c03a34e7.

spec/core/matchers/toBeNaNSpec.js

@@ -1,10 +1,11 @@
 describe("toBeNaN", function() {
-  it("passes for NaN", function() {
+  it("passes for NaN with a custom .not fail", function() {
     var matcher = j$.matchers.toBeNaN(),
       result;
 
     result = matcher.compare(Number.NaN);
     expect(result.pass).toBe(true);
+    expect(result.message).toEqual("Expected actual not to be NaN.");
   });
 
   it("fails for anything not a NaN", function() {
@@ -26,4 +27,11 @@ describe("toBeNaN", function() {
     result = matcher.compare(Number.POSITIVE_INFINITY);
     expect(result.pass).toBe(false);
   });
+
+  it("has a custom message on failure", function() {
+    var matcher = j$.matchers.toBeNaN(),
+      result = matcher.compare(0);
+
+    expect(result.message).toEqual("Expected 0 to be NaN.");
+  });
 });

src/core/matchers/toBeNaN.js

@@ -7,6 +7,12 @@ getJasmineRequireObj().toBeNaN = function(j$) {
           pass: (actual !== actual)
         };
 
+        if (result.pass) {
+          result.message = "Expected actual not to be NaN.";
+        } else {
+          result.message = "Expected " + j$.pp(actual) + " to be NaN.";
+        }
+
         return result;
       }
     };