Add PostgreSQL License information to NOTICE and selected files

NOTICE

@@ -16,8 +16,6 @@ See the License for the specific language governing permissions and
 limitations under the License.
 
 
-========================================================================
-TimescaleDB (TM)
 ========================================================================
 
                                  Apache License
@@ -223,3 +221,38 @@ TimescaleDB (TM)
    limitations under the License.
 
 
+
+========================================================================
+Certain files in this code base have been modified and/or copied,
+either partially or wholely, from source code from the PostgreSQL
+database management system, which is licensed under the open-source
+PostgreSQL License with the following copyright information.
+========================================================================
+
+
+PostgreSQL Database Management System
+(formerly known as Postgres, then as Postgres95)
+
+Portions Copyright © 1996-2018, The PostgreSQL Global Development Group
+Portions Copyright © 1994, The Regents of the University of California
+
+Permission to use, copy, modify, and distribute this software and its
+documentation for any purpose, without fee, and without a written
+agreement is hereby granted, provided that the above copyright notice
+and this paragraph and the following two paragraphs appear in all
+copies.
+
+IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
+FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
+INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND
+ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN
+ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
+INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE
+PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF
+CALIFORNIA HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE, SUPPORT,
+UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+
+========================================================================

src/plan_agg_bookend.c

@@ -5,6 +5,13 @@
  * see LICENSE-APACHE at the top level directory.
  */
 
+/*
+ * This file contains source code that was copied and/or modified from
+ * the PostgreSQL database, which is licensed under the open-source
+ * PostgreSQL License. Please see the NOTICE at the top level
+ * directory for a copy of the PostgreSQL License.
+ */
+
 /*
  *	  Optimization for FIRST/LAST aggregate functions.
  *

src/planner_import.c

@@ -4,10 +4,16 @@
  * This file is licensed under the Apache License,
  * see LICENSE-APACHE at the top level directory.
  */
+
 /*
- * This file contains functions copied verbatim from the PG core planner.
- * These function had to be copied since they were declared static in the core planner, but we need them for our
- * manipulations.
+ * This file contains source code that was copied and/or modified from
+ * the PostgreSQL database, which is licensed under the open-source
+ * PostgreSQL License. Please see the NOTICE at the top level
+ * directory for a copy of the PostgreSQL License.
+ *
+ * These function were copied from the PostgreSQL core planner, since
+ * they were declared static in the core planner, but we need them for
+ * our manipulations.
  */
 #include <postgres.h>
 #include <utils/rel.h>

src/planner_import.h

@@ -4,6 +4,17 @@
  * This file is licensed under the Apache License,
  * see LICENSE-APACHE at the top level directory.
  */
+
+/*
+ * This file contains source code that was copied and/or modified from
+ * the PostgreSQL database, which is licensed under the open-source
+ * PostgreSQL License. Please see the NOTICE at the top level
+ * directory for a copy of the PostgreSQL License.
+ *
+ * These function were copied from the PostgreSQL core planner, since
+ * they were declared static in the core planner, but we need them for
+ * our manipulations.
+ */
 #ifndef TIMESCALEDB_PLANNER_IMPORT_H
 #define TIMESCALEDB_PLANNER_IMPORT_H
 
@@ -12,12 +23,6 @@
 #include <utils/relcache.h>
 #include <utils/selfuncs.h>
 
-/*
- * This file contains functions copied verbatim from the PG core planner.
- * These function had to be copied since they were declared static in the core planner, but we need them for our
- * manipulations.
- */
-
 extern void ts_make_inh_translation_list(Relation oldrelation, Relation newrelation,
 							 Index newvarno,
 							 List **translated_vars);