Update copyright for 2018

Backpatch-through: certain files through 9.3

src/backend/utils/sort/logtape.c

@@ -64,7 +64,7 @@
  * care that all calls for a single LogicalTapeSet are made in the same
  * palloc context.
  *
- * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION

src/backend/utils/sort/sharedtuplestore.c

@@ -10,7 +10,7 @@
  * scan where each backend reads an arbitrary subset of the tuples that were
  * written.
  *
- * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION

src/backend/utils/sort/sortsupport.c

@@ -4,7 +4,7 @@
  *	  Support routines for accelerated sorting.
  *
  *
- * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION

src/backend/utils/sort/tuplesort.c

@@ -75,7 +75,7 @@
  * too many -- see the comments in tuplesort_merge_order).
  *
  *
- * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION

src/backend/utils/sort/tuplestore.c

@@ -43,7 +43,7 @@
  * before switching to the other state or activating a different read pointer.
  *
  *
- * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION