This CR covers three very small fixes all of which cause some strangeness to the verbose GC output:
a) there's one occurence in concurrentMarkThread.cpp where tty is used, instead of gclog_or_tty, when printing verbose GC output
b) doConcurrentMark() was, for some reason, incorrectly called from checkConcurrentMark (this was causing the marking phase to be incorrectly woken up after a Full GC; no marking actually happened, but marking related verbose GC information was printed which was confusing)
c) some fields of ConcurrentMark (_has_aborted, _restart_for_overflow, _concurrent_marking_in_progress, and _should_gray_objects) were not initialised. In some cases, and in conjuction with b), this was causing the marking thread to output "[GC ocnurrent-mark-restart-for-overflow]" several times a second and was bloating the GC log (which would rapidly reach the 2GB limit).