mereged in old patches for issue #225
This is a path submitted by barry.wardell@gmail.com to the google code site on issue #225 with the following message:

'I have tested these patches with the latest mercurial version and can confirm that they work fine for me.
I also find the attached patch for the high-level interface convenient.'

Shoved into git by Thomas Caswell <tcaswell@gmail.com>
re-factored prop list classes a bit.

The classes for data set creation (`PropDCID`) and group creation
(`PropGCID) now inherit from the object creation class (`PropOCID`),
which has the code for dealing with `H5P*obj_track_times`.
and required changes to pxd file