Allow UUIDs and other types of non-integer primary keys

[calexicoz]

Hi Matthew,

(In reference to #39)

Here is a starting point to integrate UUIDs. The change to lib/closure_tree/acts_as_tree.rb are pretty minimal. I copied most of the tests from tag_spec as a starting point, just to make sure everything passed. One or two had to be modified, ie array =~ array instead of array == array as the natural order of UUIDs is not necessarily the creation order.

To be honest rather than copy/pasting, I'd rather simply switch one of the existing models to UUID and keep the same tests, or use something like [Node, Tag].each {|klass| ...}.

Let me know what you think.

Also, because of the way quoting works, this should allow for binary keys as well, or other types that are neither strings nor integers.

[mceachen]

Great, thanks!

I'll merge into a new branch and see if there's a better way we can test this out, instead of duplicating the tags spec.

[calexicoz]

Cool.