[Rd] c documentation after change

[Suharto Anggono Suharto Anggono]

In R 3.4.0 RC, argument list of 'c' as S4 generic function has become
(x, ...) .
However, "S4 methods" section in documentation of 'c' (c.Rd) is not updated yet.

Also, in R 3.4.0 RC, 'c' method of class "Date" ('c.Date') is still not explicitly documented.