Consistent use of CCAssert

 * Remove @
 * Use CCAssert instead of CC_ASSERT (number of parameters differ between the two)
Remove invalid assert

 * Assert checks that width and height are > 0.0
 * However a few lines above, width and height are explicitly initialized
 * ... to 0.0
Assert implementation for Android

    * __android_log_assert is not stable
    * Uses __android_log_print instead