Minor fixes for Teensy 3.0 (and probably any other 32 bit ARM boards)

Here are several fixes for several minor issues, some preventing the library from compiling for Teensy 3.0, others just compiler warnings (when Arduino's File > Preferences is set to "show verbose").

If you would like a free Teensy 3.0 board for testing, please email directly (paul at pjrc dot com) and I'll be happy to send you one.