plugins.texi (Registering custom attributes): section renamed as (Registering custom attributes or pragmas).

2009-11-11  Basile Starynkevitch  <basile@starynkevitch.net>
	* gcc/doc/plugins.texi (Registering custom attributes): section
	renamed as (Registering custom attributes or pragmas).
	Mentions custom attributes & pragmas, and c_register_pragma, with
	a small example.
	* gcc/doc/cpp.texi (Pragmas): Mentions that plugins can provide their
	pragmas.
	* gcc/doc/extend.texi (Function Attributes): Mentions that plugin can
	provide their attributes.

From-SVN: r154097