GemPlugins and classic plugins consistency


This patch is another step in the effort of having single code-base
for GemPlugins and classic plugins. This will ease migration from
plugins to GemPlugins.

There are also few tickets regarding the other side: freezing and
unpacking gems, loading gem specific tasks and so on. I encourage you
to look (and +1 if you like) at my above patch and these following
tickets (ordering is not random):

In particular, please check #59 and the comments section - I don't
want to repeat everything, but it basically says:

"It makes sense that rake tasks loading (and generators) follow the
same logic as init.rb."