Add initial assert helpers

Closes #110

test/harness/assert.js

+function assert(mustBeTrue, message) {
+    if (mustBeTrue === true) {
+        return;
+    }
+
+    if (message === undefined) {
+        message = 'Expected true but got ' + String(truthy);
+    }
+    $ERROR(message);
+}
+
+assert._isSameValue = function (a, b) {
+    if (a === b) {
+        // Handle +/-0 vs. -/+0
+        return a !== 0 || 1 / a === 1 / b;
+    }
+
+    // Handle NaN vs. NaN
+    return a !== a && b !== b;
+};
+
+assert.sameValue = function (actual, expected, message) {
+    if (assert._isSameValue(actual, expected)) {
+        return;
+    }
+
+    if (message === undefined) {
+        message = 'Expected SameValue(' + String(actual) + ', ' + String(expected) + ') to be true';
+    }
+    $ERROR(message);
+};
+
+assert.notSameValue = function (actual, unexpected, message) {
+    if (!assert._isSameValue(actual, unexpected)) {
+        return;
+    }
+
+    if (message === undefined) {
+        message = 'Expected SameValue(' + String(actual) + ', ' + String(unexpected) + ') to be false';
+    }
+    $ERROR(message);
+};