build fails with clang, python3 and numpy 1.7.1 and higher
The build succeeds if I change
void initObjToJSON(void)
to
int initObjToJSON(void)
in objToJSON.c, but I don't know if there are repercussions.  I haven't tested with numpy 1.7 and lower.

---

$ git log
commit 51cc9d9d21554701f70ef24392bd78a3da189335
...
$ python3 -c "import numpy;print(numpy.**version**)"
1.7.1
(also fails with 1.8.0.dev-f7ea474)
$ python3 setup.py build
...
pandas/src/ujson/python/objToJSON.c:118:5: error: void function 'initObjToJSON' should not return a value [-Wreturn-type]
    import_array();
    ^~~~~~~~~~~~~~
    /Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/numpy/core/include/numpy/__multiarray_api.h:1693:144: note: expanded from macro 'import_array'
    #define import_array() {if (_import_array() < 0) {PyErr_Print(); PyErr_SetString(PyExc_ImportError, "numpy.core.multiarray failed to import"); return NUMPY_IMPORT_ARRAY_RETVAL; } }

---

from generate_numpy_api.py
# if PY_VERSION_HEX >= 0x03000000
# define NUMPY_IMPORT_ARRAY_RETVAL NULL
# else
# define NUMPY_IMPORT_ARRAY_RETVAL
# endif
# define import_array() {if (_import_array() < 0) {PyErr_Print(); PyErr_SetString(PyExc_ImportError, "numpy.core.multiarray failed to import"); return NUMPY_IMPORT_ARRAY_RETVAL; } }
