Update avrlib to compile against gcc-avr-4.7.0 toolchain

Fixes compilation error:

... must be const in order to be put into read-only section by means of
‘__attribute__((progmem))’

Remove deprecated header avr/signal.h to silence warning message.

Compilation tested on Linux Mint 14 Nadia
Fix "implicit declaration of function" warnings

Due to incomplete header inclusion.
Disable the unused rprintfProgStr() function

It causes deprecated prog_char warnings
Use macros for LCD debug printing for more readable code
Remove if block with impossible predicate