Autodetect baudrate only if either a .ino/.pde is present

Because of the way the autodetect code works, if no .ino/.pde file is
present, then the makefile hangs
Allow building with Arduino core, without a .ino/.pde file

Till not it is not possible to build with Arduino core, without using a
.ino or .pde file. This commit removes that restriction.

However, the user has to explicitly include Arduino header files.

Fix 105