Emit debug message when executing extension script.

Allows extension authors to more easily debug problems related to the
sequence of update scripts that are executed.

Discussion: https://postgr.es/m/5636a7534a4833884172fe4369d825b26170b3cc.camel%40j-davis.com
Reviewed-by: Peter Eisentraut, Nathan Bossart

Author: jeff-davis

src/backend/commands/extension.c

@@ -887,6 +887,11 @@ execute_extension_script(Oid extensionOid, ExtensionControlFile *control,
 
 	filename = get_extension_script_filename(control, from_version, version);
 
+	if (from_version == NULL)
+		elog(DEBUG1, "executing extension script for \"%s\" version '%s'", control->name, version);
+	else
+		elog(DEBUG1, "executing extension script for \"%s\" update from version '%s' to '%s'", control->name, from_version, version);
+
 	/*
 	 * If installing a trusted extension on behalf of a non-superuser, become
 	 * the bootstrap superuser.  (This switch will be cleaned up automatically