Attempt to make vcl::Timer use boost's Signals2

[Kohei Yoshida]

On Tue, 2014-11-18 at 08:20 -0500, Kohei Yoshida wrote:
> On Tue, 2014-11-18 at 23:50 +1100, Chris Sherlock wrote:
> > Hi all, 
> > 
> > 
> > I'm attempting to get Timer to use boost's Signals2. 
> 
> When you do that, could you apply "pimpl" pattern to hide its boost
> usages from the header?

If that's easily doable that is.  If not, you can just leave it and I'll
poke at that at some stage...  Either way is fine with me.

Kohei