Modified env resource to break values up by delimiter before comparing

I'd like your thoughts on this. It needs a bit of refactoring, but here is the justification for making this change:
If someone were to do (before this patch),
```ruby
windows_path 'C:\foo;C:\bar' do
  action :create
  ...
end
```
the path would grow each time this recipe was executed. This is because
compare_path would break up the current path with ;, but would not do
the same for the value being added.

Note: windows_path is just a wrapper around env that sets the delimiter to ;

cc @schisamo, @opscode/client-engineers 
I agree that the name sucks. The problem I have with changing the name is that it seems to be public, which could break other people. That being said, changing the behavior could also break people using it, so maybe this is a good time to change it.