The GCC string "Known MCU names:" was not found for non-English locale

The output of avr-gcc -Wa,-mlist-devices --target-help is parsed to find
the names of the supported MCU's. And we were relying on finding the
string "Known MCU names:". That does work anymore since it is sometines
translated. So now we simply look for lines starting with " at" of " avr".
Avoid null object in performCancel

This probably only happens in development when things got messged up.
Set Bundle-Version for de.innot.avreclipse.utils
Insert JavaSE-1.7 as the preferred Bundle-RequiredExecutionEnvironment
Start of development for 2.4.3