Hiding emphasis markers is over eager

To replicate, create a "slide" with the following:

``` org
#+BEGIN_SRC haskell
whenM :: (Monad m) => m Bool -> m () -> m ()
whenM mb mx = mb >>= \b -> when b mx
#+END_SRC
```

The slide will show

```
whenM :: (Monad m) > m Bool -> m () -> m ()
whenM mb mx = mb >> \b -> when b mx
```

Consider using the `org-hide-emphasis-markers` variable instead.
