Document new --disable-setreuid option and change description for

--disable-saved-ids to match new error message.

INSTALL

@@ -213,9 +213,11 @@ Special features/options:
   --disable-saved-ids
 	Disable use of POSIX saved IDs.  Normally, sudo will try to
 	use POSIX saved IDs if they are supported.  However, some
-	implementations are broken.  If sudo aborts with an error like:
-	    "seteuid(0): Operation not permitted"
-	you probably need to disable POSIX saved ID support.
+	implementations are broken.
+
+  --disable-setreuid
+	Disable use of the setreuid() function for operating systems
+	where it is broken.  4.4BSD has setreuid() but it doesn't really work.
 
   --disable-sia
 	Disable SIA support.  This is the "Security Integration Architecture"