remove l33t tests

Summary: I looked for 31337 in their tests and killed them

Reviewed By: @JoelMarcey

Differential Revision: D1497162
typechecker: Allow `foreach (X as list(...))`.

Summary: Fixes T2744848.

This patch actually allows any lvalue in the `as` position, so `as $a[0]`
typechecks as well. (HHVM accepts any lvalue as well.)

Also allows `foreach (X as $k => list(...))`.

Reviewed By: @elgenie

Differential Revision: D1486266
Add TreadHashMap support to `idx`

Reviewed By: @markw65

Differential Revision: D1496938
Better error-handling for gdb `idx`

Summary: Try to recognize when a container is empty, and also don't balk when we
encounter unknown types (so that `idx` can be used without an hhvm
binary).

Reviewed By: @jano

Differential Revision: D1497178
Support std::unordered_set for gdb `idx`

Summary: Yesssss

Reviewed By: @jano

Differential Revision: D1497183