Fix a build problem(Apple LLVM version 6.0 / clang-600.0.56).

```
$ make
gcc -o InputSourceSelector -Wall InputSourceSelector.m -framework Carbon -framework Foundation
InputSourceSelector.m:13:58: warning: 'NSObject' attribute may be put on a typedef only; attribute
      is ignored [-WNSObject-attribute]
        for (TISInputSourceRef __attribute__((NSObject)) inputSource in inputSources) {
                                                         ^
InputSourceSelector.m:13:9: error: selector element type 'TISInputSourceRef' (aka
      'struct __TISInputSource *') is not a valid object
        for (TISInputSourceRef __attribute__((NSObject)) inputSource in inputSources) {
        ^    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 warning and 1 error generated.
make: *** [InputSourceSelector] Error 1
```