Warn when using checked map arrays with array_splice

Reviewed By: @paroski

Differential Revision: D1489522
Updated twig to 1.16.0 in the framework tests

Summary: The **current** twig tests differ from the expected output when run. This seams to be due to the numerical locale test. Maybe we should exclude that test? I have in my pull, and I've also updated us to 1.16.0.

The diff showing the flakey test **without** any of my modifications to the expected output or framework.yml:
```
----------------------
Twig_Tests_CompilerTest::testReprNumericValueWithLocale

RUN TEST FILE:  cd /root/hhvm/hphp/test/frameworks/framework_downloads/twig && /root/hhvm/hphp/test/frameworks/../../hhvm/hhvm -v Repo.Local.Mode=-- -v Repo.Central.Path=/tmp/framework-test8uvGFo --config /root/hhvm/hphp/test/frameworks/php.ini -c /root/hhvm/hphp/test/frameworks/.generated.php.ini /root/hhvm/hphp/test/frameworks/vendor/bin/phpunit --debug  -c /root/hhvm/hphp/test/frameworks/framework_downloads/twig/phpunit.xml.dist --filter 'Twig_Tests_CompilerTest::testReprNumericValueWithLocale'

EXPECTED: .
>>>>>>>
ACTUAL: S
```
Closes https://github.com/facebook/hhvm/pull/3370

Reviewed By: @fredemmott

Differential Revision: D1487074

Pulled By: svcscm