Fix compilation of Cosa outside of Arduino IDE

I have been able to identify this issue compiling Cosa outside of the Arduino IDE on both Mac (10.9.1) with avr-gcc (4.8.2/4.7.2) and Ubuntu (13.10) with avr-gcc (4.7.2). Conditionally defining __PROGMEM in Types.hh fixes the issue for both platforms without affecting Arduino (1.0.5)