Changed assertEqual to assertEquals

Changed the SimpleTest backward compatible assertEqual assertions to PHPUnits assertEquals.

http://simpletest.org/api/SimpleTest/UnitTester/UnitTestCase.html#assertEqual
http://phpunit.de/manual/current/en/appendixes.assertions.html#appendixes.assertions.assertEquals

It seems the tests already adhered to the parameter order of the assertEquals method signature:
assertEquals(mixed $expected, mixed $actual[, string $message = ''])

All other used assertion methods are part of the PHPUnit framework:
assertTrue
assertFalse
assertEmpty
assertSame
assertInternalType
http://phpunit.de/manual/current/en/appendixes.assertions.html#appendixes.assertions.assertInternalType