Spell "partitionwise" consistently.

I'm not sure which spelling is better, "partitionwise" or "partition-wise",
but everywhere else we spell it "partitionwise", so be consistent.

Tatsuro Yamada reported the one in README, I found the other one with grep.

Discussion: https://www.postgresql.org/message-id/d25ebf36-5a6d-8b2c-1ff3-d6f022a56000@lab.ntt.co.jp

contrib/postgres_fdw/expected/postgres_fdw.out

@@ -8435,7 +8435,7 @@ SELECT t1.a,t1.b FROM fprt1 t1, LATERAL (SELECT t2.a, t2.b FROM fprt2 t2 WHERE t
  400 | 400
 (4 rows)
 
--- with PHVs, partition-wise join selected but no join pushdown
+-- with PHVs, partitionwise join selected but no join pushdown
 EXPLAIN (COSTS OFF)
 SELECT t1.a, t1.phv, t2.b, t2.phv FROM (SELECT 't1_phv' phv, * FROM fprt1 WHERE a % 25 = 0) t1 FULL JOIN (SELECT 't2_phv' phv, * FROM fprt2 WHERE b % 25 = 0) t2 ON (t1.a = t2.b) ORDER BY t1.a, t2.b;
                       QUERY PLAN                      

contrib/postgres_fdw/sql/postgres_fdw.sql

@@ -2291,7 +2291,7 @@ EXPLAIN (COSTS OFF)
 SELECT t1.a,t1.b FROM fprt1 t1, LATERAL (SELECT t2.a, t2.b FROM fprt2 t2 WHERE t1.a = t2.b AND t1.b = t2.a) q WHERE t1.a%25 = 0 ORDER BY 1,2;
 SELECT t1.a,t1.b FROM fprt1 t1, LATERAL (SELECT t2.a, t2.b FROM fprt2 t2 WHERE t1.a = t2.b AND t1.b = t2.a) q WHERE t1.a%25 = 0 ORDER BY 1,2;
 
--- with PHVs, partition-wise join selected but no join pushdown
+-- with PHVs, partitionwise join selected but no join pushdown
 EXPLAIN (COSTS OFF)
 SELECT t1.a, t1.phv, t2.b, t2.phv FROM (SELECT 't1_phv' phv, * FROM fprt1 WHERE a % 25 = 0) t1 FULL JOIN (SELECT 't2_phv' phv, * FROM fprt2 WHERE b % 25 = 0) t2 ON (t1.a = t2.b) ORDER BY t1.a, t2.b;
 SELECT t1.a, t1.phv, t2.b, t2.phv FROM (SELECT 't1_phv' phv, * FROM fprt1 WHERE a % 25 = 0) t1 FULL JOIN (SELECT 't2_phv' phv, * FROM fprt2 WHERE b % 25 = 0) t2 ON (t1.a = t2.b) ORDER BY t1.a, t2.b;

src/backend/optimizer/README

@@ -1106,8 +1106,8 @@ PartitionSchemeData object.  This reduces memory consumed by
 PartitionSchemeData objects and makes it easy to compare the partition schemes
 of joining relations.
 
-Partition-wise aggregates/grouping
+Partitionwise aggregates/grouping
-----------------------------------
+---------------------------------
 
 If the GROUP BY clause has contains all of the partition keys, all the rows
 that belong to a given group must come from a single partition; therefore,