Fix tablespace inheritance for partitioned rels

Commit ca4103025d left a few loose ends.  The most important one
(broken pg_dump output) is already fixed by virtue of commit
3b23552ad8, but some things remained:

* When ALTER TABLE rewrites tables, the indexes must remain in the
  tablespace they were originally in.  This didn't work because
  index recreation during ALTER TABLE runs manufactured SQL (yuck),
  which runs afoul of default_tablespace in competition with the parent
  relation tablespace.  To fix, reset default_tablespace to the empty
  string temporarily, and add the TABLESPACE clause as appropriate.

* Setting a partitioned rel's tablespace to the database default is
  confusing; if it worked, it would direct the partitions to that
  tablespace regardless of default_tablespace.  But in reality it does
  not work, and making it work is a larger project.  Therefore, throw
  an error when this condition is detected, to alert the unwary.

Add some docs and tests, too.

Author: Álvaro Herrera
Discussion: https://postgr.es/m/CAKJS1f_1c260nOt_vBJ067AZ3JXptXVRohDVMLEBmudX1YEx-A@mail.gmail.com

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201904072
+#define CATALOG_VERSION_NO	201904251
 
 #endif

src/include/commands/tablespace.h

@@ -49,7 +49,7 @@ extern Oid	AlterTableSpaceOptions(AlterTableSpaceOptionsStmt *stmt);
 
 extern void TablespaceCreateDbspace(Oid spcNode, Oid dbNode, bool isRedo);
 
-extern Oid	GetDefaultTablespace(char relpersistence);
+extern Oid	GetDefaultTablespace(char relpersistence, bool partitioned);
 
 extern void PrepareTempTablespaces(void);
 

src/include/nodes/parsenodes.h

@@ -2154,6 +2154,8 @@ typedef struct Constraint
 	List	   *options;		/* options from WITH clause */
 	char	   *indexname;		/* existing index to use; otherwise NULL */
 	char	   *indexspace;		/* index tablespace; NULL for default */
+	bool		reset_default_tblspc;	/* reset default_tablespace prior to
+										 * creating the index */
 	/* These could be, but currently are not, used for UNIQUE/PKEY: */
 	char	   *access_method;	/* index access method; NULL for default */
 	Node	   *where_clause;	/* partial index predicate */
@@ -2769,6 +2771,8 @@ typedef struct IndexStmt
 	bool		transformed;	/* true when transformIndexStmt is finished */
 	bool		concurrent;		/* should this be a concurrent index build? */
 	bool		if_not_exists;	/* just do nothing if index already exists? */
+	bool		reset_default_tblspc;	/* reset default_tablespace prior to
+										 * executing */
 } IndexStmt;
 
 /* ----------------------