Faster partition pruning

Add a new module backend/partitioning/partprune.c, implementing a more
sophisticated algorithm for partition pruning.  The new module uses each
partition's "boundinfo" for pruning instead of constraint exclusion,
based on an idea proposed by Robert Haas of a "pruning program": a list
of steps generated from the query quals which are run iteratively to
obtain a list of partitions that must be scanned in order to satisfy
those quals.

At present, this targets planner-time partition pruning, but there exist
further patches to apply partition pruning at execution time as well.

This commit also moves some definitions from include/catalog/partition.h
to a new file include/partitioning/partbounds.h, in an attempt to
rationalize partitioning related code.

Authors: Amit Langote, David Rowley, Dilip Kumar
Reviewers: Robert Haas, Kyotaro Horiguchi, Ashutosh Bapat, Jesper Pedersen.
Discussion: https://postgr.es/m/098b9c71-1915-1a2a-8d52-1a7a50ce79e8@lab.ntt.co.jp

src/backend/partitioning/Makefile

@@ -0,0 +1,17 @@
+#-------------------------------------------------------------------------
+#
+# Makefile--
+#    Makefile for backend/partitioning
+#
+# IDENTIFICATION
+#    src/backend/partitioning/Makefile
+#
+#-------------------------------------------------------------------------
+
+subdir = src/backend/partitioning
+top_builddir = ../../..
+include $(top_builddir)/src/Makefile.global
+
+OBJS = partprune.o
+
+include $(top_srcdir)/src/backend/common.mk