added xor function to misc.py as jtag.py was failing to import it, JTAG speed improvement

It seems that JTAG is broken because of this missing function. The version on my hard drive had it.

I have the JTAG code successfully loading bitstreams into Xilinx Kintex 7 and Spartan 3A FPGAs. The Kintex 7 results in a 24 Mb write_dr. I could commit some example code and my XilinxFPGA class.