Server side deleting of nodes.

Support custom ExtensionObjects

Revert previously deleted ExtensionObject class.

fix suport for Dimensions

Improved loading performance when using cached address spaces

Close generated address space files once the code generation is done

Use cPickle (basically a C-implementation of the already used pickle
mechanism) and ensure that the highest protocol version is used to
improve the loading performance.

Not closing the generated files may cause some errors when trying
to interpret the files in the same script later on (i.e. parsing errors due
to half written files).