[Rd] Alternative to some recently changed parts of dates.R and datetime.R

[Suharto Anggono Suharto Anggono]

In function 'Summary.Date' in dates.R ,
..1
could be used instead of
...elt(1L)

In function 'format.POSIXlt' in datetime.R ,
unlist(unclass(x)[1L:3L], use.names=FALSE)
could be used instead of
unlist(`names<-`(unclass(x)[1L:3L], NULL))
Also, the fragment
secs <- x$sec[f0]; secs <- secs[is.finite(secs)]
could be put inside
if(np >= 1L)