Testing has demonstrated that del self.x does not make the memory used to
store x available for garbage collection.
There is clearly an additional reference from another place. In fact
*after* del self.x then the memory can be made available for GC by
assignment (e.g. self.x = None). However I haven't found how to release
this reference and there is nothing in self.__dict__ that can help.
For now we'll use a twp-step process where we set the variable to None
before deleting it.
This has a big impact on memory usage. For Software it is almost 1k
(a.k.a. about 10% impact on free RAM).
Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>