fixes build with clang

This PR fixes build errors on OS X using.

BTW: I've created a [homebrew](http://brew.sh/) formula for this: https://gist.github.com/chrmoritz/9846074
(install it with `brew install https://gist.githubusercontent.com/chrmoritz/9846074/raw/starstructor.rb`)

Starstructor starts on OS X but doesn't render a proper gui: 
![bildschirmfoto 2014-03-29 um 02 05 49](https://cloud.githubusercontent.com/assets/1686759/2556769/5a035f0a-b6de-11e3-93bd-a325e6bda952.png)

Log: 
```
"[02:05:21 201] Opened log file at /usr/local/Cellar/starstructor/0.1/starstructor.app/Contents/MacOS/logs/03-29-2014_02-05-21_starstructor.txt" 
"[02:05:21 201] Scanning for all files in A:/Development/starbound with extensions: .object .material .npc .structure .dungeon .world .shipworld" 
"[02:05:21 201] Scanning complete in 0ms. 0 files found." 
"[02:05:21 201] 0 assets to be loaded." 
"[02:05:21 202] 0 assets loaded in 0 ms, 0 assets invalid." 
"[02:05:22 207] 56 frames in 1004ms." 
...
```
(maybe some filesystem releated issues, at least A:/Development/starbound doesn't look good)

I try to look at it, if I have time.