x86: shutdown on LPM_POWERDOWN
make: OSX: don't fail for empty .a archives

Fixes issue #1333.
tests/Travis: run unittests on x86, too
Merge pull request #1252 from Kijewski/travis-x86

tests/Travis: run unittests on qemu-i386, too
Merge pull request #1334 from Kijewski/issue-1333

make: OSX: don't fail for empty .a archives
boards:telosb: fix comment
boards:wsn430-v14: harmonise cc2420_isr
boards:z1: fix comment