[Rd] read.ssd (foreign) 'wishes': enable long variable names, add output object to windows example

[gcbooma]

Hello,

A couple of quick 'wishes' for read.ssd in the foreign package:

1) Enable long variable names by adding 'options validvarname=v6;' line
directly before doing 'proc copy', e.g. (from my own alteration of
read.ssd):
    #export the data
    st7 <- "options validvarname=v6;\n"
    st8 <- paste("proc copy in=src2rd out=rd;\n")
    st9 <- paste("select", "tempfile", ";\n", sep = " ")
...and corresponding 'cat' to 'tmpProg', of course.

2) Add output object to windows example in the help file. In v0.8-15
help file for 'foreign', no object is indicated, causing R to kill the
output if run as-is - potentially confusing for newbies.

Thank you for this useful function!

-Greg