Reloading C++ modules each time a node executes

Per Jim, in previous versions of GPI PyMOD extensions would be re-loaded each time a node ran. This meant you could run `gpi_make` in the background and immediately use the new changes. The current behavior is not the same — now you have to re-launch GPI to use the newly compiled extension. I'm not sure if this is always consistent as I thought sometimes refreshing or re-placing the node would work, as did using the "imp.reload()" function in the node.

Ideal behavior: PyMOD extensions are re-loaded each time a node executes OR when a node is refreshed/replaced.