rtl.texi (Arithmetic): Rewrite entries for PLUS, SS_PLUS, US_PLUS, LO_SUM, MINUS, SS_MINUS, US_MINUS.

	* doc/rtl.texi (Arithmetic): Rewrite entries for PLUS,
	SS_PLUS, US_PLUS, LO_SUM, MINUS, SS_MINUS, US_MINUS.

From-SVN: r76735