Make geopandas work with Python 3.3.

1. Support Py3K build with automatic 2to3 run. This was tested with Python 3.3. Note, the changeset is about build and installation only (not running geopandas yet).

2. When running read_postgis function, I am getting
```
Traceback (most recent call last):
  File "script.py", line 51, in <module>
    data = GeoDataFrame.from_postgis(QUERY, db, geom_col='location', index_col='timestamp')
  File "/home/user/.local/lib/python3.3/site-packages/geopandas-0.1.0.dev_1edddad-py3.3.egg/geopandas/geodataframe.py", line 211, in from_postgis
  File "/home/user/.local/lib/python3.3/site-packages/geopandas-0.1.0.dev_1edddad-py3.3.egg/geopandas/io/sql.py", line 39, in read_postgis
  File "/home/user/.local/lib/python3.3/site-packages/pandas-0.13.1-py3.3-linux-x86_64.egg/pandas/core/series.py", line 2023, in apply
    mapped = lib.map_infer(values, f, convert=convert_dtype)
  File "inference.pyx", line 920, in pandas.lib.map_infer (pandas/lib.c:43334)
  File "/home/user/.local/lib/python3.3/site-packages/geopandas-0.1.0.dev_1edddad-py3.3.egg/geopandas/io/sql.py", line 39, in <lambda>
AttributeError: 'str' object has no attribute 'decode'
```
The 2nd commit replaces str.decode('hex') call with unhexlify function call, which should make geopandas work on both Python 2.6 and Python 3.3.