Delay type inference of lambdas.

Summary: See code comments.

I think this fixes https://github.com/facebook/hhvm/issues/2787.

There's a larger problem where we don't raise a warning if we're
unsuccessful in inferring the concrete type of a lambda's parameters.
This patch simply reduces the number of cases where we are unsuccessful.

Reviewed By: @jwatzman, @elgenie

Differential Revision: D1582361
Fix handling of exit() in nast_terminality

Reviewed By: @elgenie

Differential Revision: D1590318
Set $name and $class properties in reflection to "public" to leave __get and __set methods free for inheritance

Summary: fixes #2684
Closes https://github.com/facebook/hhvm/pull/3848

Reviewed By: @paulbiss

Differential Revision: D1578197
Fix some typos and "formatos".

Summary: Closes https://github.com/facebook/hhvm/pull/3891

Reviewed By: @paulbiss

Differential Revision: D1588549