Name of DateTime extension should be date

Summary: `extension_loaded("date")` should be `true`
`extension_loaded("datetime")` should be `false`
Fixes #4403

Reviewed By: @paulbiss

Differential Revision: D1724162

Signature: t1:1724162:1418000963:d4dd6b8ab074ec07fb3e896fcbad6153d22b39a3
Add 64-bit packing and unpacking

Summary: PHP 5.6.3 added 64-bit flags for packing and unpacking. It was noticed that we
haven't supported this yet. So now we are.

Fixes #4296

Reviewed By: @paulbiss

Differential Revision: D1696014

Signature: t1:1696014:1418001230:10f4fe28b4ced5d925d254b256dd209bbc6068b0
Update vfsstream to v1.4.0

Summary: Update framework test to use vfsstream v1.4.0.
Remove vfsStreamWrapperWithoutRootTestCase from blacklist.
Closes https://github.com/facebook/hhvm/pull/4402

Reviewed By: @JoelMarcey

Differential Revision: D1724142

Signature: t1:1724142:1418011683:f757f792574d0e886129375d8edd821a9f6388da