core: align stack on a 32bit boundary

Fixes #1267.
thirdparty_import merge
uart: implement IRQ based UART rx for stm32f1
Merge remote-tracking branch 'kijewski/issue-1267' into bnb
HACK: fix off by one for CC1100
HACK: remove printf from clist
make: compile msba2 boards with -O0
sixlowpan: some additional debugging
IMPORT: thomas' AT driver changes
HACK: some hacks to fix alignmend trouble in net_if
ccnl: additional debug in appserver
HACK: try to fix alignments