Add script to upgrade v0.90.0 to v0.91.0.

sql/pgtap--0.90.0--0.91.0.sql

@@ -0,0 +1,27 @@
+DO $$
+BEGIN
+    IF pg_version_num() < 9.0 THEN
+        EXECUTE $E$
+            CREATE FUNCTION pg_tablespace_location(
+                OID
+            ) RETURNS TEXT LANGUAGE SQL AS $F$
+                SELECT spclocation
+                  FROM pg_catalog.pg_tablespace
+                 WHERE OID = $1;
+            $F$;
+        $E$;
+    END IF;
+END;
+$$;
+
+CREATE OR REPLACE FUNCTION has_tablespace( NAME, TEXT, TEXT )
+RETURNS TEXT AS $$
+    SELECT ok(
+        EXISTS(
+            SELECT true
+              FROM pg_catalog.pg_tablespace
+             WHERE spcname = $1
+               AND pg_tablespace_location(oid) = $2
+        ), $3
+    );
+$$ LANGUAGE sql;