Add scw _userdata SERVER KEY=@path/to/file support "à-la-curl"

[moul]

Expected result:

$  cat <<EOF > test.txt
heredoc> first line
heredoc> second line
heredoc> third line
heredoc> EOF
$  scw _userdata alpine [email protected]
test
$  scw _userdata alpine test
first line
second line
thirt line
$

See http://curl.haxx.se/docs/manpage.html#-d

[QuentinPerez]

#184