Introducing Atmel toolchain 3.4.4

This PR introduces Atmel toolchain 3.4.4 (see http://distribute.atmel.no/tools/opensource/Atmel-AVR-GNU-Toolchain/3.4.4/)
WRT to previous release (3.4.3), binutils has been upgraded to 2.24 and gdb has been added to the list of available command line tools

Be aware: this PR will be **rebased** from time to time.