THRIFT: mutex trylock support

Summary: add trylock support to the Mutex class

Reviewed By: mcslee

Test Plan: added trylock mutexes to foreman, walked through them in gdb
(behaved correctly) and then ran an entire sweep (behaved correctly)

Notes: slee ftw


git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@665204 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/lib/cpp/src/concurrency/Mutex.h b/lib/cpp/src/concurrency/Mutex.h
index 02accf9..72f7525 100644
--- a/lib/cpp/src/concurrency/Mutex.h
+++ b/lib/cpp/src/concurrency/Mutex.h
@@ -20,6 +20,7 @@
   Mutex();
   virtual ~Mutex() {}
   virtual void lock() const;
+  virtual bool trylock() const;
   virtual void unlock() const;
 
  private: