Cursor x axis value is not shown when using regular timeseries
Hi,

you should be able to paste the following snippet in a ipython --pylab session

``` python
import pandas
index = pandas.date_range(start='2001-1-1', end='2001-1-10', freq='D')
ts = pandas.TimeSeries(index=index, data=index.day)
figure()
ts.plot()
figure()
ts[:3].append(ts[6:]).plot()
```

Although the labelling is definitely nicer in the regular timeseries case, the cursor x axis value is not shown (bottom right corner with the tk pylab backend)
http://imgur.com/WCe6P,o8jge#0:

The irregular timeseries with the standard matlplotlib plot_date labelling does show a value for the cursor x axis value:
http://imgur.com/WCe6P,o8jge#1

I tried with the qt backend and I get the same results so it appears to be backend independent.

Not a huge deal but I find the cursor x axis value quite useful from time to time when interactively inspecting a plot (zooming, panning, etc...).
