Differences between function and keywords for savefig.bbox and axes.facecolor

For at least two rcparams the name is surprisingly different from corresponding keyword.

```
 rcParams['savefig.bbox'] = x -> savefig(..., bbox_inches=x)
 rcParams['axes.facecolor']  = x correct for ax.patch but fig.add_axes(bgcolor=x)
```

I think at least in the second case the keyword should be changed to facecolor for
consistency.
