In r240466, when Greg added the jThreadsInfo packet, he accidentally

disabled the use of the jThreadGetExtendedInfo packet which is used
to retrieve additional information about a thread, such as the QoS
setting for that thread on darwin systems.  

Re-enable the use of the jThreadGetExtendedInfo packet, and add 
some quick tests to the TestQueues mac test case which will verify
that we can retrieve the QoS names for these test threads.

<rdar://problem/22925096> 

llvm-svn: 250364