support pandas Series as input for lat/lon -> x/y conversion

Nobody has claimed this yet.

Using `pd.Series()` as input for lat/long -> x/y conversion does currently raise a RuntimeError:

``` python
x,y = map_katins(df["lon"], df["lat"])
RuntimeError Traceback (most recent call last)
in ()
15 # map_katins.plot(x, y, "ro", markersize=10)
16 x,y = map_katins(df["lon"].values, df["lat"].values)
---> 17 x,y = map_katins(df["lon"], df["lat"])
18 map_katins.plot(x, y, "o", color="grey", markersize=5)
19

C:\portabel\miniconda\envs\katins\lib\site-packages\mpl_toolkits\basemap\__init__.pyc in __call__(self, x, y, inverse)
1146 except TypeError:
1147 y = [_dg2rad*yy for yy in y]
-> 1148 xout,yout = self.projtran(x,y,inverse=inverse)
1149 if self.celestial and inverse:
1150 try:

C:\portabel\miniconda\envs\katins\lib\site-packages\mpl_toolkits\basemap\proj.pyc in __call__(self, *args, **kw)
284 outxy = self._proj4(xy, inverse=inverse)
285 else:
--> 286 outx,outy = self._proj4(x, y, inverse=inverse)
287 if inverse:
288 if self.projection in ['merc','mill','gall']:

C:\portabel\miniconda\envs\katins\lib\site-packages\mpl_toolkits\basemap\pyproj.pyc in __call__(self, *args, **kw)
386 _proj.Proj._inv(self, inx, iny, radians=radians, errcheck=errcheck)
387 else:
--> 388 _proj.Proj._fwd(self, inx, iny, radians=radians, errcheck=errcheck)
389 # if inputs were lists, tuples or floats, convert back.
390 outx = _convertback(xisfloat,xislist,xistuple,inx)

_proj.pyx in _proj.Proj._fwd (src/_proj.c:1571)()

RuntimeError:
```

Using

``` python
x,y = map_katins(df["lon"].values, df["lat"].values)
```

works...

``` python
import mpl_toolkits.basemap
mpl_toolkits.basemap.__version__
'1.0.7'
```

Start by reproducing the failure at the map_katins(df["lon"], df["lat"]) entry point and compare it with the working .values calls, using the Basemap 1.0.7 context provided. Trace the conversion into the Basemap projection call and identify the existing regression-test location; done means pandas Series inputs convert without the RuntimeError while existing array inputs continue to work.

Written by the indexing model from the issue text.