QwtPlotSpectrogram and contour text labels .... try this.

G'day All,

(Second try for this. The first blocked by zip file. Now using a tar.gz
file.)

Uwe or Josef: Feel free to add any aspects of this code to the base
QwtPlotSpectrogram if you think it is useful.

A while back I asked the group about text labels for the
QwtPlotSpectrogram and found, while this had not been done yet, it was
something that was on the list of things to do.

I have just spent a few days looking into this and have written and
extender class to QwtPlotSpectrogram that will add contour text labels
called LabelledSpectrogram. To test it out I have modified the
QwtPlotSpectrogram example and added another contour plot over the top
of the example (i.e. two contour diagrams in the one plot; something I
need to do). The code is in early development, but I have attached it
for anyone to have a look at, use or make comment on. Included in the
code is a sample PNG file on what it should look like.

Features of LabelledSpectrogram
-------------------------------
* Contour labels may be positions based on label placement bit flags.
Any combination of the flags may be enabled. The options are:
  * N_PER_LEVEL: Display 'N' labels per contour level evenly spaced
(sort of); default is 2 per level.
  * AT_MIN_X:    Display a label at the minimum X value for each
contour.
  * AT_MAX_X:    Display a label at the maximum X value for each