Error registering / unregistering font file.
Hey. Cool project.

Everything was working great for about 2 weeks, then I started getting this error:

`Error Domain=com.apple.CoreText.CTFontManagerErrorDomain Code=105 "Could not register the font file(s)"`

So, I checked out error code 105 -> kCTFontManagerErrorAlreadyRegistered

I looked through Iconic's source and it doesn't look like the "already registered" case was handled, so I thought I'd just handle it myself in the app delegate by unregistering the font first:

``` swift
let bundle = NSBundle(forClass: Iconic.self)
if let url = bundle.URLForResource("Linearicons", withExtension: "ttf"){
       var error: Unmanaged<CFErrorRef>? = nil
       CTFontManagerUnregisterFontsForURL(url, .None, &error)
       Iconic.registerIconFont()
}
```

However, the call to CTFontManagerUnregisterFontsForURL also returns an error:

`Error Domain=com.apple.CoreText.CTFontManagerErrorDomain Code=201 "Could not unregister the font file(s)"`

So, I checkout out error code 201 -> kCTFontManagerErrorNotRegistered

Not registered... o.O

Have you run into this before - not being able to register nor unregister a font? Tried cleaning, deleting my derived data, deleting the simulator's data, and double checked the font urls, but no luck. 

Could Iconic try to continue its initialization in the case when the error is 105 - already registered?

Any suggestions appreciated.

Thanks!
