Implement wordwrap() natively

Reviewed By: @ptarjan

Differential Revision: D1440874
Fix Redis::sRandMember()

Summary: Don't require a second parameter which is originally optional.
Also, it shouldn't always return an array.

Closes: #3213
Closes #3217
Created from: https://github.com/facebook/hhvm/pull/3217

Reviewed By: @swtaarrs

Differential Revision: D1442294