Fix checker bug.
Fix checker bug.

src/cpu/checker/thread_context.hh:
    Checker's TC should only copy state, and not fully take over from the old context (prevents it from accidentally stealing the quiesce event).

hoangt/tpzsimul.gem5,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,hoangt/tpzsimul.gem5,pombredanne/http-repo.gem5.org-gem5-,hoangt/tpzsimul.gem5,hoangt/tpzsimul.gem5,vovojh/gem5,vovojh/gem5,hoangt/tpzsimul.gem5,hoangt/tpzsimul.gem5,hoangt/tpzsimul.gem5,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-