add support to track number of rows being returned on bulk-loading of GpuScan
bugfix: infinite loop to alloc result buffer and kernel call in GpuHashJoin

see bug #68
workaround: pg_crc32_table is moved to __global area, instead of __constant
fixbug: various pointers were not updated on expand_multihash_tables()

expand_multihash_tables() tries to allocate twice large amount of
multi hash-tables using alloc() and free() form, so delivered
pointers that referenced old region, but we didn't update it.
Eventually, it leads random buffer corruption because hash
construction peformed on the buffer already released!
Merge branch 'master' into preagg