soft delete using id that does not exist in db

The current implementation will try to create a new record when id is
not in the database.  Included are a test that demonstrates this issue
and a fix.

Note: Model->read() actually returns false, not array(), when a record
is not found.
http://api.cakephp.org/2.1/class-Model.html#_read
Improved efficiency for models with associations

Clear the 'modified' and 'updated' fields before deleting so they will
be updated.
Merge pull request #71 from larryb82/develop

soft delete using id that does not exist in db