Fix the 'markbit' bug of cache-adapt multicoregc version. In the compact phase,...

Fix the 'markbit' bug of cache-adapt multicoregc version.  In the compact phase, some cores might need to move some local objects to some other remote cores.  There could be cache incoherent problem caused by the mark bit.  To fix it, in the mark phase, whenever the mark bit is changed, flush it to the main memory and after the mark phase is finished add a 'barrier' before starting the compact phase