[nem-en] Bugs in extension method implementation

[vc]

      > In case of /greedy- the current loading strategy suffices. But in
case
      > of /greedy-  we should load assemblies in two stages: first only
read
      > the assemblies 
      
      +1
      
      > and search for Extension attribute in them and then
      > load types.
      
      By name? In fact before loading all assemblies IsDefined() will not
work.
      
      > This will take some time to do, but I think it is worth doing
anyway.
      
      +1