[O] exported html: src block missing pseudo-elements

[Manuel Koell]

I exported some html with defaut style and a javascript src block:

```
#+BEGIN_SRC javascript
var x = {}
#+END_SRC
```

The exported html contains the default styles and pseudo-elements for
following languages only:

```

  pre.src:hover:before { display: inline;}  pre.src-sh:before    {
content: 'sh'; }  pre.src-bash:before  { content: 'sh'; }
pre.src-emacs-lisp:before { content: 'Emacs Lisp'; }  pre.src-R:before
    { content: 'R'; }  pre.src-perl:before  { content: 'Perl'; }
pre.src-java:before  { content: 'Java'; }  pre.src-sql:before   {
content: 'SQL'; }

```

Why is javascript not included? I know I could write the
`pre.src-javascript:before { content: 'Javascript'; } myself.
Syntax-highlighting looks fine but the upper right label on hover is
missing.

Thanks!