Duemilanove compatibility

Here are some changes, to make the slave compile under Linux (at least Ubuntu 12.04) without the IDE:

- I added a configure script that creates the actual Makefile depending on which board the user selects (e.g. atmega328 for the Duemilanove) and features (e.g. --with-lcd5110).
- I fixed some const and stray character problems that occured with my gcc version.

For it to work, the "official" Makefile needs to be installed. On Ubuntu it's easily possible with `apt-get install arduino-core arduino-mk`. The same one is supposed to work on Mac and the configure script also respects that but apparently I cannot check that.