Invalid calculation of MINfloat16/MAXfloat16 in pandas/algos.pyx
The code generated by Cython from pandas/algos.pyx contains an undefined behavior (invalid cast of floating-point number to integer):

```
easy_install -U Cython
git clone git://github.com/pydata/pandas.git
python setup.py install
```

The generated code for the line from `pandas/algos.pyx`

``` python
cdef np.float16_t MINfloat16 = np.NINF
```

in `pandas/algos.c` contains:

``` c
typedef npy_float16 __pyx_t_5numpy_float16_t;
//... more code
__pyx_t_5numpy_float16_t __pyx_t_10;
//... more code
__pyx_t_10 = __pyx_PyFloat_AsFloat(__pyx_t_1);
```

The file `numpy-1.9.2-py2.7-linux-x86_64.egg/numpy/core/include/numpy/npy_common.h`
defines `npy_float16` as 16-bit _integer_ type (I guess numpy implementation has a custom code that carefully represents these 16 bits as mantiss+exponent). Casting floating-point value `-inf` to a 16-bit integer type is an undefined behavior according to C standard.

I wasn't able to find any place in pandas code that uses `MINfloat16` (and `MAXfloat16`). Is it safe to just delete them?
