Summary: For heaps larger than 32Gb, the number of heap regions overflows the data type used to hold the region index in the SparsePRT structure. Changed the region indexes, card indexes, and RSet hash table buckets to ints and added some size overflow guarantees.
Reviewed-by: ysr, tonyp

Summary: The _expanded flag of the sparse RSets is not reset and this can leave a RSet in an inconsistent state if it is expanded more than once. Also, we should be iterating over the _cur, instead of the _next, sparse table
Reviewed-by: apetrusenko, iveresov

Summary: First mercurial integration of the code for the Garbage-First garbage collector.
Reviewed-by: apetrusenko, iveresov, jmasa, sgoldman, tonyp, ysr