Simplify EMFILE behavior.

Separating "what to traverse" from "how to traverse and what to do with it "
in findModulePath.  It may also fix one not-yet-found bug (absolute ids
weren't loaded when dirs.length = 0).

This reverts commit 083ee0f8.

V8 build broken on cygwin:
  ./deps/v8/src/handles.h:62: instantiated from `T*
  v8::internal::Handle<T>::operator->() const [with T = v8::internal::Code]'
  ./deps/v8/src/accessors.cc:396: instantiated from here
  ./deps/v8/src/handles-inl.h:50:
  error: call of overloaded `BitCast(v8::internal::Code** const&)' is
  ambiguous
  ./deps/v8/src/utils.h:732: note: candidates are: Dest
  v8::internal::BitCast(const Source&) [with Dest = v8::internal::Code**,
  Source = v8::internal::Code**]
  ./deps/v8/src/utils.h:743:
  note:                 Dest v8::internal::BitCast(Source* const&) [with Dest
  = v8::internal::Code**, Source = v8::internal::Code*]
  scons: *** [obj/release/accessors.o] Error 1

This will only manipulate the OS X-level process name, not the title shown
in e.g. ps.

Some platforms require SO_REUSEPORT to be set for the socket.

Plus some minor cosmetic corrections

- [lib/dns.js] dns.lookup takes a new optional argument "family" which
  should be the integer 4, 6, dns.AF_INET or dns.AF_INET6. Passing a
  non-false "family" argument makes c-ares explicitly look up addresses for
  the specified family.

- [test/simple/test-c-ares.js] test explicit address family lookups

Regression.