Revert "Remove obsolete pg_show_plans--1.0.sql file"

This reverts commit 6a17adc.

We'll leave the file around in the repository for testing upgrades, but
don't install it.

pg_show_plans--1.0.sql

@@ -0,0 +1,48 @@
+/* pg_show_plans/pg_show_plans--1.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION pg_show_plans" to load this file. \quit
+
+-- Register functions.
+CREATE FUNCTION pg_show_plans_enable()
+RETURNS void
+AS 'MODULE_PATHNAME'
+LANGUAGE C;
+
+CREATE FUNCTION pg_show_plans_disable()
+RETURNS void
+AS 'MODULE_PATHNAME'
+LANGUAGE C;
+
+CREATE FUNCTION pgsp_format_json()
+RETURNS void
+AS 'MODULE_PATHNAME'
+LANGUAGE C;
+
+CREATE FUNCTION pgsp_format_text()
+RETURNS void
+AS 'MODULE_PATHNAME'
+LANGUAGE C;
+
+CREATE FUNCTION pg_show_plans(
+    OUT pid int8,
+    OUT level int8,
+    OUT userid oid,
+    OUT dbid oid,
+    OUT plan text
+)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME'
+LANGUAGE C;
+
+-- Register a view on the function for ease of use.
+CREATE VIEW pg_show_plans AS
+  SELECT * FROM pg_show_plans();
+
+GRANT SELECT ON pg_show_plans TO PUBLIC;
+
+-- Don't want this to be available to non-superusers.
+REVOKE ALL ON FUNCTION pg_show_plans_enable() FROM PUBLIC;
+REVOKE ALL ON FUNCTION pg_show_plans_disable() FROM PUBLIC;
+REVOKE ALL ON FUNCTION pgsp_format_json() FROM PUBLIC;
+REVOKE ALL ON FUNCTION pgsp_format_text() FROM PUBLIC;