Replace unsafe OR REPLACE clause and issue a recommendation for installation in a non-public scheme.

For more information, see the documentation:
37.17.6.2. Security Considerations for Extension Scripts (https://www.postgresql.org/docs/current/extend-extensions.html#EXTEND-EXTENSIONS-SECURITY)
5.9.6. Usage Patterns (https://www.postgresql.org/docs/current/ddl-schemas.html#DDL-SCHEMAS-PATTERNS)

Author: kulaginm

README.md

@@ -95,11 +95,14 @@ shared_preload_libraries = 'pg_pathman'
 
 It is essential to restart the PostgreSQL instance. After that, execute the following query in psql:
 ```plpgsql
-CREATE EXTENSION pg_pathman;
+CREATE SCHEMA pathman;
+CREATE EXTENSION pg_pathman WITH SCHEMA pathman;
 ```
 
 Done! Now it's time to setup your partitioning schemes.
 
+> **Security notice**: Do not install pg_pathman in public schemas! Specify the schema explicitly using the WITH SCHEMA clause. Installing an extension in a scheme that is accessible to malicious users can lead to a privilege escalation attack.
+
 > **Windows-specific**: pg_pathman imports several symbols (e.g. None_Receiver, InvalidObjectAddress) from PostgreSQL, which is fine by itself, but requires that those symbols are marked as `PGDLLIMPORT`. Unfortunately, some of them are not exported from vanilla PostgreSQL, which means that you have to either use Postgres Pro Standard/Enterprise (which includes all necessary patches), or patch and build your own distribution of PostgreSQL.
 
 ## How to update

hash.sql

@@ -3,15 +3,15 @@
  * hash.sql
  *		HASH partitioning functions
  *
- * Copyright (c) 2015-2016, Postgres Professional
+ * Copyright (c) 2015-2020, Postgres Professional
  *
  * ------------------------------------------------------------------------
  */
 
 /*
  * Creates hash partitions for specified relation
  */
-CREATE OR REPLACE FUNCTION @[email protected]_hash_partitions(
+CREATE FUNCTION @[email protected]_hash_partitions(
 	parent_relid		REGCLASS,
 	expression			TEXT,
 	partitions_count	INT4,
@@ -53,7 +53,7 @@ SET client_min_messages = WARNING;
  *
  * lock_parent - should we take an exclusive lock?
  */
-CREATE OR REPLACE FUNCTION @[email protected]_hash_partition(
+CREATE FUNCTION @[email protected]_hash_partition(
 	old_partition		REGCLASS,
 	new_partition		REGCLASS,
 	lock_parent			BOOL DEFAULT TRUE)
@@ -146,7 +146,7 @@ $$ LANGUAGE plpgsql;
 /*
  * Just create HASH partitions, called by create_hash_partitions().
  */
-CREATE OR REPLACE FUNCTION @[email protected]_hash_partitions_internal(
+CREATE FUNCTION @[email protected]_hash_partitions_internal(
 	parent_relid		REGCLASS,
 	attribute			TEXT,
 	partitions_count	INT4,
@@ -158,14 +158,14 @@ LANGUAGE C;
 /*
  * Calculates hash for integer value
  */
-CREATE OR REPLACE FUNCTION @[email protected]_hash_part_idx(INT4, INT4)
+CREATE FUNCTION @[email protected]_hash_part_idx(INT4, INT4)
 RETURNS INTEGER AS 'pg_pathman', 'get_hash_part_idx'
 LANGUAGE C STRICT;
 
 /*
  * Build hash condition for a CHECK CONSTRAINT
  */
-CREATE OR REPLACE FUNCTION @[email protected]_hash_condition(
+CREATE FUNCTION @[email protected]_hash_condition(
 	attribute_type		REGTYPE,
 	attribute			TEXT,
 	partitions_count	INT4,