fix ubuntu 12.04 compilation error on clientCheck.ml

Summary: ```
Linking CXX static library libhphp_analysis.a
[ 39%] Built target hphp_analysis
File "clientCheck.ml", line 266, characters 30-314:
Error: This expression has type string but an expression was expected of type
         ('a, out_channel, unit) format =
           ('a, out_channel, unit, unit, unit, unit) format6
make[5]: *** [clientCheck.cmx] Error 2
make[4]: *** [rec.opt] Error 1
make[3]: *** [opt] Error 2
make[2]: *** [hphp/hack/CMakeFiles/hack] Error 2
make[1]: *** [hphp/hack/CMakeFiles/hack.dir/all] Error 2
make: *** [all] Error 2
```
Closes https://github.com/facebook/hhvm/pull/4172

Reviewed By: @jwatzman

Differential Revision: D1667392

Signature: t1:1667392:1415395945:9498622a05067d6cffca64fe706d2e2d0ac3a4cb
TEventBase -> folly::EventBase

Summary: This is now in folly

Reviewed By: @djwatson

Differential Revision: D1665731

Signature: t1:1665731:1415392441:28f793e0b87eb6c7ffbabb9343ebbcf3afcd8d0b
Remove WorkerThread shim

Summary: This has moved.

Reviewed By: @viswanathgs

Differential Revision: D1667183

Signature: t1:1667183:1415397345:438b6a5c4208ca4b928dc83790125aaa010a65a5