[Rd] minor (possibly documentation) bug in seq

[Deepayan Sarkar]

With today's r-devel, help(seq) says:

     The last generates the sequence '1, 2', ..., 'length(along)',
     unless the argument is of length 1 when it is interpreted as a
     'length' argument.

referring to the usage 

     seq(along)

This is not true for 0:

> seq(0)
[1] 1 0
> seq(length = 0)
numeric(0)

I'm not sure what the intended behaviour of seq(0) is, but either seq() or the 
help page should be fixed.

Also, the exception (naturally) holds only for _numeric_ arguments of length 
1. 

Deepayan