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=

Committed: https://crrev.com/75e43a6681e01de9422a0211f502723d23b51247
Cr-Commit-Position: refs/heads/master@{#30103}

[saper, 2015-08-08 13:02:00]

saper@marcincieslak.com changed reviewers:
+ yangguo@chromium.org

[saper, 2015-08-08 13:03:39]

saper@marcincieslak.com changed reviewers:
+ machenbach@google.com

[Yang, 2015-08-08 13:11:03]

The CQ bit was checked by yangguo@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-08-08 13:11:07]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1277353002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1277353002/1

[commit-bot: I haz the power, 2015-08-08 13:35:34]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-08 13:35:35]

Dry run: This issue passed the CQ dry run.

[Yang, 2015-08-11 07:21:10]

On 2015/08/08 13:35:35, commit-bot: I haz the power wrote:
> Dry run: This issue passed the CQ dry run.

lgtm.

[Yang, 2015-08-11 07:21:25]

On 2015/08/11 07:21:10, Yang wrote:
> On 2015/08/08 13:35:35, commit-bot: I haz the power wrote:
> > Dry run: This issue passed the CQ dry run.
> 
> lgtm.

CLA check passes btw.

[Yang, 2015-08-11 07:21:28]

The CQ bit was checked by yangguo@chromium.org

[commit-bot: I haz the power, 2015-08-11 07:21:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1277353002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1277353002/20001

[commit-bot: I haz the power, 2015-08-11 07:48:55]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-08-11 07:49:10]

Patchset 2 (id:??) landed as
https://crrev.com/75e43a6681e01de9422a0211f502723d23b51247
Cr-Commit-Position: refs/heads/master@{#30103}