Repair python3 build under Homebrew Python 3.4 with OSX 10.9.

Environment

```bash
$ uname -a
Darwin whale.local 13.2.0 Darwin Kernel Version 13.2.0: Thu Apr 17 23:03:13 PDT 2014; root:xnu-2422.100.13~1/RELEASE_X86_64 x86_64
$ brew info python3
python3: stable 3.4.1 (bottled), HEAD
https://www.python.org/
/usr/local/Cellar/python3/3.4.1 (3994 files, 68M) *
  Poured from bottle
From: https://github.com/Homebrew/homebrew/commits/master/Library/Formula/python3.rb
==> Dependencies
Build: pkg-config ✔
Required: openssl ✔
Recommended: readline ✔, sqlite ✔, gdbm ✔, xz ✔
```

Output

```bash
$ make pythonmodule3
...
python3 setup.py build
running build
running build_ext
building 'miniupnpc' extension
creating build
creating build/temp.macosx-10.9-x86_64-3.4
clang -I/usr/local/Cellar/python3/3.4.1/Frameworks/Python.framework/Versions/3.4/include/python3.4m -c miniupnpcmodule.c -o build/temp.macosx-10.9-x86_64-3.4/miniupnpcmodule.o
miniupnpcmodule.c:602:9: error: non-void function 'PyInit_miniupnpc' should
      return a value [-Wreturn-type]
        return;
        ^
1 error generated.
error: command 'clang' failed with exit status 1
make: *** [pythonmodule3] Error 1
```