Fixes for Rails 3.2.* and some refactors

* upgrade AR gem dependency to 3.0.10
* use update_all instead of update_attribute in delete() and restore!() so update callbacks aren't run before/after deleting & restoring record
* don't overwrite destroyed? b/c it's only for in-memory records; keep deleted? to check for deleted_at existence
* revert recent addition of persisted? overwrite; there are other places in AR where persisted? is called, so let's just set @destroyed instead
* remove test for to_param; Rails 3.2.3 would use ActiveModel#to_param implementation instead, which checks for persisted? before stringifying