Add parallel aggregate support

Also add various functions to allow cross type operators to save having to
cast lesser types up to fixeddecimal.

Please note that the upgrade script to upgrade from 1.0.0 to 1.1.0 is currently
only for 9.6 and beyond. If you're running XL or 9.5 or less this script will
need to be altered.

Author: david-rowley

contrib/fixeddecimal/Makefile

@@ -3,11 +3,18 @@ OBJS = fixeddecimal.o
 
 EXTENSION = fixeddecimal
 AGGSTATESQL := $(shell pg_config --version | grep -qE "XL" && echo fixeddecimalaggstate.sql)
-AGGFUNCSSQL := $(shell pg_config --version | grep -qE "XL" && echo fixeddecimal--xlaggs.sql || echo fixeddecimal--aggs.sql)
-BRINSQL := $(shell pg_config --version | grep -qE "9\.[5-9]| 10\.0" && echo fixeddecimal--brin.sql)
-SQLFILES := $(shell cat $(AGGSTATESQL) fixeddecimal--1.0.0_base.sql $(AGGFUNCSSQL) $(BRINSQL) > fixeddecimal--1.0.0.sql)
+AGGFUNCSSQL := $(shell pg_config --version | grep -qE "XL" && echo fixeddecimal--xlaggs.sql)
 
-DATA = fixeddecimal--1.0.0.sql
+AGGFUNCSSQL := $(shell pg_config --version | grep -qE "9\.[6-9]| 10\.[0-9]" && echo fixeddecimal--parallelaggs.sql || echo fixeddecimal--aggs.sql)
+
+BRINSQL := $(shell pg_config --version | grep -qE "9\.[5-9]| 10\.[0-9]" && echo fixeddecimal--brin.sql)
+
+# 9.6 was the dawn of parallel query, so we'll use the parallel enabled .sql file from then on.
+BASESQL := $(shell pg_config --version | grep -qE "9\.[6-9]| 10\.[0-9]" && echo fixeddecimal--1.1.0_base_parallel.sql || echo fixeddecimal--1.1.0_base.sql)
+
+SQLFILES := $(shell cat $(AGGSTATESQL) $(BASESQL) $(AGGFUNCSSQL) $(BRINSQL) > fixeddecimal--1.1.0.sql)
+
+DATA = fixeddecimal--1.1.0.sql fixeddecimal--1.0.0--1.1.0.sql
 
 MODULES = fixeddecimal