As reported by Duncan Booth at
http://permalink.gmane.org/gmane.comp.python.general/551183 the new
@spam.getter syntax modifies the property in place but it should create
a new one.

The patch is the first draft of a fix. I've to write unit tests to
verify the patch. It copies the property and as a bonus grabs the
__doc__ string from the getter if the doc string initially came from the
getter as well.