Makefiles and library modified to add a new F_CLOCK constant to give the unprescaled master input clock frequency, so that the correct PLL mask can be determined even when the CPU (F_CPU) clock rate is prescaled outside the normal input range of the PLL.

Started to clean up the AVRISP Programmer project code, donated by Opendous Inc.

USBtoSerial demo now discards all Rx data when not connected to a USB host, rather than buffering characters for transmission next time the device is attached to a host.