lat_0, lon_0 ignored

I am trying to set up Basemap to use a Cylindrical Equal Area projection and to place the origin at a specific lat/lon (this is to match some input x/y data that uses a false easting/northing), but it seems that setting the `lat_0` and `lon_0` parameters does nothing.

``` python
from mpl_toolkits.basemap import Basemap

# Oklahoma bounds
# ('o' = origin at corner of Kingfisher/Logan/Canadian/Oklahoma counties)
lats = {'n': 37.1, 's': 33.6, 'c': 35.5, 'o': 35.726}
lons = {'e': -94.4, 'w': -103.0, 'c': -97.5, 'o': -97.674}

buf = 0.05 # plot buffer size (in degrees)

res = 'c' # map shapes resolution

# projection parameters
proj = 'cea' # cylindrical equal area
lat_ts = lats['c'] # true scale at geographic center
lon_0 = lons['o'] # x=0 at counties corner
lat_0 = lats['o'] # y=0 at counties corner

m = Basemap(projection = proj, lat_ts = lat_ts, resolution = res,
lon_0 = lon_0, lat_0 = lat_0,
urcrnrlon = lons['e'] + buf, urcrnrlat = lats['n'] + buf,
llcrnrlon = lons['w'] - buf, llcrnrlat = lats['s'] - buf*4)
```

Then checking the origin gives:

```
In [15]: m(0, 0, inverse=True)
Out[15]: (-103.05000000000305, 33.399999999963455)
```

...which is the lower-left corner of the map bounds, not the coordinates I gave for `lat_0` and `lon_0`. I get the same output if I leave out `lat_0` and `lon_0` entirely.

At first, I thought maybe the CEA projection doesn't support these parameters and that I should just shift my data manually, but the docs claim that `lat_0` and `lon_0` are used by all projections to set the origin.

As a workaround, I can set an offset to get the intended results:

``` python
offset = m(lon_0, lat_0)
df['x'], df['y'] = (df.x + offset[0], df.y + offset[1]) # where df is a Pandas dataframe with my data
```

Note: Originally posted to StackOverflow, where I was encouraged to move the issue here. http://stackoverflow.com/questions/31302427/lat-0-lon-0-ignored-by-basemap

Start with the Basemap projection setup and coordinate-conversion entry points, then run the supplied Cylindrical Equal Area example with and without lat_0 and lon_0. Verify whether m(0, 0, inverse=True) honors the supplied origin instead of returning the lower-left map bounds; done means the behavior matches the documented parameters or the limitation is clearly established.

Written by the indexing model from the issue text.