main.c : print out '<stdin>' and '<stdout>' instead of '-' when using
stdio for I/O.
Thanks to Francisco T. A. Silva <ftas@geodigitus.com.br> for catching
this, and the error fixed by the previous commit as well.
git-svn-id: svn://svn.savannah.nongnu.org/avrdude/trunk@325 81a1dc3b-b13d-400b-aceb-764788c761c2