Update and lock framework test dependencies

Summary: This updates the framework testing dependencies, and this locking of dependencies should be better than the previous way of specifying less than half of the exact versions in the composer.json.
Closes https://github.com/facebook/hhvm/pull/3411

Reviewed By: @ptarjan

Differential Revision: D1489052

Pulled By: @fredemmott
Adds a couple tests requested in my previous diff

Summary: Followup to D1496765, adds test cases related to overriding methods with different memoization attributes. These cases were requested by@fredemmott

Reviewed By: @jano

Differential Revision: D1502087
Introduce kVPackedKind for vector-like arrays

Summary: This diff introduces a new ArrayKind kVPackedKind which is vector-like
(with integer keys 0 thru n-1) and is able to gracefully downgrade into a
PackedArray.

Reviewed By: @elgenie

Differential Revision: D1483853
Parser support for "varray(..)"

Summary: This diff adds HHVM support for "varray(..)" literals in "<?hh" files, and
it removes hphp_varray().

Depends on D1483853

Reviewed By: @elgenie

Differential Revision: D1502673
Force hhi root to be set in master before workers fork

Summary: Make sure that the workers all get the same, preset hhi path,
computed by the master before they fork. This could manifest as a worker
trying to re-extract the hhi files to a preexisting location (since the
random seed is shared across all of them) and hitting an exception when
the directory already exists.

It's pretty weird that we didn't run into this immediately when I did
the hhi embedding -- AFAICT this has been wrong since day one. I think
what saved us is the logic that says "if the number of changes is lower
than N, do it all in the master", where N is about 10 -- so most of the
time this didn't matter. (And it looks like during init we do some other
stuff in the master too or something? In any event, this was hard to
trigger.)

Reviewed By: @elgenie

Differential Revision: D1501184
Print backtrace when worker dies

Summary: On an unhandled exception, we were printing the exception name
but not the backtrace. Do that too, so we have some hope of knowing what
went wrong.

Reviewed By: @elgenie

Differential Revision: D1501129