Add a version for zsh 4.3.11.

This version has been added because zsh 4.3.11 as installed on Mountain Lion (and possibly earlier) is broken. It is missing the zsh/pcre zmodule. When you do:

```
zmodload zsh/pcre
```

You get the following error:

```
zsh: failed to load module `zsh/pcre': dlopen(/usr/lib/zsh/4.3.11/zsh/pcre.so, 9): image not found
```

The solution on a [Japanese blog][1] was to build zsh 5.0 through homebrew and then install the pcre.so into /usr/lib/zsh/4.3.11/zsh. While I am comfortable with the concept of the solution, I'm not as comfortable mixing the versions so cavalierly, even though I suspect the ABI has not changed.

Since I have copied the zsh 5.0 formula, this also means that the gdbm module is also available.

Given the purpose behind this build, it is keg-only.

[1]: http://inputxoutput.com/pcre-image-not-found/