Applying a quick fix for "prog_char is deprecated" warning

Applying a quick fix for "prog_char is deprecated" warning
in Arduino. As 'prog_char' is completely removed in later
versions of avr-gcc/g++, people with Ubuntu 14.04 won't be
able to build Arduino out of the box because of this. This
commit clears up some warnings AND allows Ubuntu 14.04 to
build our stack for Arduino (However, the question as to
whether we should update our versions of Ubuntu and/or
Arduino are still up in the air.).

Majorly, this enables Shamit to keep moving along. He is
currently making sure all of our documentation for building
the stack for Arduino is up to par. He will also be seeing
how far our current stack will take us (i.e. will it work on
other embedded devices without any further mods?).

Change-Id: I9a079b7211082e3d3fd418dd5162aaa606a8fc04