added cancan gem
tweaked cancan defaults (we don't have current_user)
First cut of a set of permissions
sorta kinda works, but login/homepage are b0rked
this seems to mostly work
Added more informative error message.
redirect to previous page if available
modified views to use CanCan
Tried to get controller tests passing.

All are fine except for plantings.  I'm pretty sure hte problem is to do
with these two lines in app/model/ability.rb

  can :update, Planting, :garden => { :owner_id => member.id }
  can :destroy, Planting, :garden => { :owner_id => member.id }

I'm pretty sure that's the right syntax (according to
https://github.com/ryanb/cancan/wiki/Defining-Abilities) but since it's
the update and delete actions that are failing, I guess I must have it
wrong somehow.  Any hints?
I'd rather not use Member.new
that can? check was superflous; controller does it for us.
controller tests for plantings now pass
Merge pull request #101 from Skud/spike-cancan

Controller security