Allow nulling of derived type variables in python

Assigning a derived type value to None in python causes it to be
nullified.
Cleanup of set and getpointer routines

Added prototypes for them.
Renamed them to setscalarpointer, getscalarpointer and same for array.
Cleaned up the argument naming to be more consistent.
Changed setscalarpointers to grabscalarpointers, etc.
Removed references to obsolete machines
Removed f90 option since it is always true