Modified PosixThreadFactory

Modified PosixThreadFactory
        Added explicit detached getter and setter
Modified PosixThreadFactory::~PThread:
        Check for join failing and don't transition to detached_ state if it does.  Potential thread-handle leak for
        threads created joinable who aren't referenced by any external thread.  Solution for now has to be
        "DONT DO THAT", the clever approach doesn't always work.

Added ThreadFactoryTests.floodNThreads:
        Loop M times for N threads where M x N is bigger than 32K to verify that detached threads can be created
        ad infinitum.

Reviewed By: mcslee

Revert Plan: revertible

Test Plan: concurrency_test thread-factory passes

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@665130 13f79535-47bb-0310-9956-ffa450edef68