NEST: added fails_with for {clang,llvm}-6.0

Version 2.2.2 fails to build with both clang as well as llvm-gcc v6.0
CAVEAT: even with brew'd gcc, `make install` fails
-> with gcc-4.9 on OSX 10.9.5 Mavericks
NEST: bumped to current release 2.4.2

Confirmed to build with gcc-4.9.2 (bottled)