Improve consistency of comments in system catalog headers.

Use the term "system catalog" rather than "system relation" in assorted
places where it's clearly referring to a table rather than, say, an
index.  Use more natural word order in the header boilerplate, improve
some of the one-liner catalog descriptions, and fix assorted random
deviations from the normal boilerplate.  All purely neatnik-ism, but
why not.

John Naylor, some additional cleanup by me

Discussion: https://postgr.es/m/CAJVSVGUeJmFB3h-NJ18P32NPa+kzC165nm7GSoGHfPaN80Wxcw@mail.gmail.com

Author: tglsfdc

src/backend/catalog/genbki.pl

@@ -535,8 +535,8 @@ sub gen_pg_attribute
 	{
 		my $table = $catalogs{$table_name};
 
-		# Currently, all bootstrapped relations also need schemapg.h
-		# entries, so skip if the relation isn't to be in schemapg.h.
+		# Currently, all bootstrap catalogs also need schemapg.h
+		# entries, so skip if it isn't to be in schemapg.h.
 		next if !$table->{schema_macro};
 
 		$schemapg_entries{$table_name} = [];
@@ -769,7 +769,7 @@ sub form_pg_type_symbol
 {
 	my $typename = shift;
 
-	# Skip for rowtypes of bootstrap tables, since they have their
+	# Skip for rowtypes of bootstrap catalogs, since they have their
 	# own naming convention defined elsewhere.
 	return
 	  if $typename eq 'pg_type'

src/include/catalog/pg_aggregate.dat

@@ -1,7 +1,7 @@
 #----------------------------------------------------------------------
 #
 # pg_aggregate.dat
-#    Initial contents of the pg_aggregate system relation.
+#    Initial contents of the pg_aggregate system catalog.
 #
 # Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
 # Portions Copyright (c) 1994, Regents of the University of California

src/include/catalog/pg_aggregate.h

@@ -1,7 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * pg_aggregate.h
- *	  definition of the system "aggregate" relation (pg_aggregate)
+ *	  definition of the "aggregate" system catalog (pg_aggregate)
  *
  *
  * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group

src/include/catalog/pg_am.dat

@@ -1,7 +1,7 @@
 #----------------------------------------------------------------------
 #
 # pg_am.dat
-#    Initial contents of the pg_am system relation.
+#    Initial contents of the pg_am system catalog.
 #
 # Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
 # Portions Copyright (c) 1994, Regents of the University of California

src/include/catalog/pg_am.h

@@ -1,7 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * pg_am.h
- *	  definition of the system "access method" relation (pg_am)
+ *	  definition of the "access method" system catalog (pg_am)
  *
  *
  * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group

src/include/catalog/pg_amop.dat

@@ -1,7 +1,7 @@
 #----------------------------------------------------------------------
 #
 # pg_amop.dat
-#    Initial contents of the pg_amop system relation.
+#    Initial contents of the pg_amop system catalog.
 #
 # Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
 # Portions Copyright (c) 1994, Regents of the University of California

src/include/catalog/pg_amop.h

@@ -1,7 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * pg_amop.h
- *	  definition of the system "amop" relation (pg_amop)
+ *	  definition of the "access method operator" system catalog (pg_amop)
  *
  * The amop table identifies the operators associated with each index operator
  * family and operator class (classes are subsets of families).  An associated

src/include/catalog/pg_amproc.dat

@@ -1,7 +1,7 @@
 #----------------------------------------------------------------------
 #
 # pg_amproc.dat
-#    Initial contents of the pg_amproc system relation.
+#    Initial contents of the pg_amproc system catalog.
 #
 # Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
 # Portions Copyright (c) 1994, Regents of the University of California

src/include/catalog/pg_amproc.h

@@ -1,7 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * pg_amproc.h
- *	  definition of the system "amproc" relation (pg_amproc)
+ *	  definition of the "access method procedure" system catalog (pg_amproc)
  *
  * The amproc table identifies support procedures associated with index
  * operator families and classes.  These procedures can't be listed in pg_amop

src/include/catalog/pg_attrdef.h

@@ -1,7 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * pg_attrdef.h
- *	  definition of the system "attribute defaults" relation (pg_attrdef)
+ *	  definition of the "attribute defaults" system catalog (pg_attrdef)
  *
  *
  * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group