Pragma disable 4716 for CL: abort doesn't return.
Evade signed-unsigned comparison warning.
Looks like NULL turns into an untyped 0 on cl (somehow).
Introduce wali::util::unordered_map/set which currently wraps
boost::unordered_map/set, remove uses of tr1::unordered_map/set,
which caused compile problems on some Linuxes.