Error message with hobby package

I am trying to use the hobbypackage with this minimal example from the manual:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{hobby}
\begin{document}
\begin{tikzpicture}[scale=.5,use Hobby shortcut]
\draw (0,0) .. (6,4) .. (4,9) .. (1,7) .. (3,5) .. cycle;
\end{tikzpicture}
\end{document}

On compiling with pdflatex I get this error message:

! Undefined control sequence.
\hobby_genpath: ...y }\prg_stepwise_function:nnnN
{0}{1}{\l_hobby_npoints_in...
l.7 .... (6,4) .. (4,9) .. (1,7) .. (3,5) .. cycle
;

I am using TeXLive 2012 and the hobby.code.tex that came with it.

What can I do to get it working?

P.S. Googling came up with a message on the Italian TeX Group forum but I could not cotton on to what was being said.

-
Essentially, egreg in this post explained that the function \prg_stepwise_function:nnnN has been substituted by \int_step_function:nnnN; I used the workaround suggested by him, for example, in my last edit to How can I draw an egg using TikZ?. –  Claudio Fiandrino Apr 25 '13 at 10:10
@Claudio Fiandrino: thanks for the explanation and that link: it was real fun! –  chandra Apr 25 '13 at 11:12