Fix RSpec 3.x deprecations

[lime]

The failure_message_for_should syntax is deprecated in RSpec 3.

This could of course be merged into the rails3 branch as well. Do you want me to make a separate pull request for that?

[radar]

Thanks for this @lime. The code looks good to me. I should be able to merge it just fine into the rails3 branch,

[lime]

Awesome! Also, if I may bug you, could we get a version 2.0.3 at some point? ;)

[radar]

I'll release 2.0.3 once #102 is fixed.

[schlick]

Sadly, the RSpec 2 compatibility doesn't work for me with RSpec 2.14 (and paranoia 2.0.3). I get:

undefined method failure_message'`

I'll have a play around and see if I can easily get it to work.

[lime]

Hm, I realise now that I might have messed up... 😬 I thought I tried it out with RSpec 2 as well but, embarrassingly, I may have forgotten.

I'll have time to debug it later in the week, unless you manage to fix it before that. ;)

[schlick]

I had a play around with it but I couldn't get something satisfactory. In the end I monkey patched it in my app.

[lime]

#197 should do the trick. Sorry about that. :)