revise initialization of khentry
bugfix: isnull_array/values_array on multihashnode was not correctly built
bugfix: fix a problem if GpuHashJoin took a bulk-load from GpuScan

This fix contains both of outer_attrefs bitmap handing and not-null
constraint handling.
bugfix: pgstrom_create_kern_parambuf() incorrectly set up kern_parambuf

If Param value has no special data type, it continues the loop without
increment index of array. In the result, it remains uninitialized data
on the tail of array.
bugfix: unexpected assertion failed on tcache_create_tchead()

when no columns are referenced in the query, typically COUNT(*),
gpuscan tries to create empty tcache (actually, it contains only
system attributes). But assertion check assumed cached_attrs
bitmap is not NULL.
bugfix: expand_multihash_tables() incorrectly set maxlen, then it may cause buffer overrun because of longer 'maxlen' than actually assigned.
Merge branch 'master' into preagg
a workaround commit