Fix lchown when no user found

Summary: Also add appropriate warnings

Increases Symfony from 89.68 to 89.8
Closes https://github.com/facebook/hhvm/pull/4194

Reviewed By: @JoelMarcey

Differential Revision: D1669950

Signature: t1:1669950:1415808530:a050c547474714b230cccd9cfd3d638160743d0f
Try to catch more information about a problem

Summary: The bug isn't this code, but this is where it crashes.  Add an assert
and hopefully we'll get more info.

Reviewed By: @alexmalyshev

Differential Revision: D1674370
Preserve index of sockets passed into/out-of socket_select()

Summary: Active sockets should remain at the offset they were at
on the way into the function call.  HHVM is currently renumbering
them from zero.

Closes #2698

Reviewed By: @JoelMarcey

Differential Revision: D1673788

Signature: t1:1673788:1415741539:0f295abe094e63076726f4101d8c74647f17a38b