Local partitioned indexes

When CREATE INDEX is run on a partitioned table, create catalog entries
for an index on the partitioned table (which is just a placeholder since
the table proper has no data of its own), and recurse to create actual
indexes on the existing partitions; create them in future partitions
also.

As a convenience gadget, if the new index definition matches some
existing index in partitions, these are picked up and used instead of
creating new ones.  Whichever way these indexes come about, they become
attached to the index on the parent table and are dropped alongside it,
and cannot be dropped on isolation unless they are detached first.

To support pg_dump'ing these indexes, add commands
    CREATE INDEX ON ONLY <table>
(which creates the index on the parent partitioned table, without
recursing) and
    ALTER INDEX ATTACH PARTITION
(which is used after the indexes have been created individually on each
partition, to attach them to the parent index).  These reconstruct prior
database state exactly.

Reviewed-by: (in alphabetical order) Peter Eisentraut, Robert Haas, Amit
	Langote, Jesper Pedersen, Simon Riggs, David Rowley
Discussion: https://postgr.es/m/20171113170646.gzweigyrgg6pwsg4@alvherre.pgsql

src/include/nodes/parsenodes.h

@@ -839,7 +839,7 @@ typedef struct PartitionRangeDatum
 } PartitionRangeDatum;
 
 /*
- * PartitionCmd - info for ALTER TABLE ATTACH/DETACH PARTITION commands
+ * PartitionCmd - info for ALTER TABLE/INDEX ATTACH/DETACH PARTITION commands
  */
 typedef struct PartitionCmd
 {
@@ -2702,6 +2702,10 @@ typedef struct FetchStmt
  * index, just a UNIQUE/PKEY constraint using an existing index.  isconstraint
  * must always be true in this case, and the fields describing the index
  * properties are empty.
+ *
+ * The relation to build the index on can be represented either by name
+ * (in which case the RangeVar indicates whether to recurse or not) or by OID
+ * (in which case the command is always recursive).
  * ----------------------
  */
 typedef struct IndexStmt
@@ -2709,6 +2713,7 @@ typedef struct IndexStmt
 	NodeTag		type;
 	char	   *idxname;		/* name of new index, or NULL for default */
 	RangeVar   *relation;		/* relation to build index on */
+	Oid			relationId;		/* OID of relation to build index on */
 	char	   *accessMethod;	/* name of access method (eg. btree) */
 	char	   *tableSpace;		/* tablespace, or NULL for default */
 	List	   *indexParams;	/* columns to index: a list of IndexElem */