Resistors on DE2 board switches

@banenky, Resistors directly connected with FPGAs are a common practice in FPGA board design. As DWH said, they are used to idiot proof the design in case the pin is operated at low level. Another explanation can be that even the pins are set as output pins, these resistors could be used as current limiting resistors for driving any sensitive ICs connected to the FPGA. Normally it isn't needed with the dedicated clock input pins but safety comes first. It's better to have them in your design rather than leaving them out.