6920090: G1: Disable ReduceInitialCardMarks at least until 6920109 is fixed
Summary: G1 now answers "no" to the query can_elide_initializing_store_barrier() in the product build. A debug flag allows alternate behaviour in debug builds.
Reviewed-by: iveresov, tonyp
6919980: G1: remove +UseG1GC from under experimental options (second attempt)
Summary: Trying this again, as the original change was lost.
Reviewed-by: ysr, jmasa