Use static_cast<> for NULL (clang 3.7)

Use static_cast<> for NULL (clang 3.7)

The following errors come up when compiling v8
 with clang 3.7 on FreeBSD/amd64:

src/runtime/runtime-i18n.cc:629:37: error: reinterpret_cast from
'nullptr_t' to 'v8::internal::Smi *' is not allowed
  local_object->SetInternalField(1, reinterpret_cast<Smi*>(NULL));
                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

test/cctest/test-heap.cc:131:20: error: reinterpret_cast from
      'nullptr_t' to 'v8::internal::Object *' is not allowed
  Handle<Object> n(reinterpret_cast<Object*>(NULL), isolate);
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test/cctest/test-heap.cc:1989:18: error: reinterpret_cast from
      'nullptr_t' to 'Address' (aka 'unsigned char *') is not
      allowed
  Address base = reinterpret_cast<Address>(NULL);
                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

+add myself to the AUTHORS file.

BUG=

Review URL: https://codereview.chromium.org/1277353002

Cr-Commit-Position: refs/heads/master@{#30103}