fixbug on multihash_copy_plan and some cleanup
Merge branch 'master' of github.com:kaigai/pg_strom
fixbug: overflow might happen on numeric->integer translation
bugfix: again, gpuscan_try_replace_seqscan_plan pulls-up qualifier correctly.

Once plan is constructed, SeqScan node has node->qual in extracted form,
so no need to try to extract qualifier from RestrictInfo again.
Merge branch 'master' into numeric