tor: additional optional deps

An additional optional dep for Tor.

Also removes the example file, as upstream regenerate it periodically and currently we don’t seem to respect that regeneration and leave outdated sample files in etc.

Adds a set of caveats about the ` torrc ` file, similar to the ones we have for ` clamav ` and others.
Apparently not. Unless I actively delete the file it doesn't get replaced. I still had the file from September in there. I'll double check the non-Yosemite bottles in a bit to make sure it's not just a bottling kink again.

Sent from my iPhone

> On 27 Dec 2014, at 10:03, Mike McQuaid <notifications@github.com> wrote:
> 
> In Library/Formula/tor.rb:
> 
> > @@ -31,6 +33,12 @@ def install
> >      args << "--with-libnatpmp-dir=#{Formula["libnatpmp"].opt_prefix}" if build.with? "libnatpmp"
> >      args << "--with-libminiupnpc-dir=#{Formula["miniupnpc"].opt_prefix}" if build.with? "miniupnpc"
> >  
> > +    # The example file is regenerated by upstream periodically and we should respect that.
> > +    # Note that this won't remove any torrc file the user has currently installed, only the sample.
> > +    if File.exist? etc/"tor/torrc.sample"
> > +      rm etc/"tor/torrc.sample"
> > +    end
> Will it not just be rewritten on make install?
> 
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