move the compat include into the lazy-load

before this patch when trying to use knife-vault  knife encrypt would throw errors because a method was added to compat.rb that assumes the class has been loaded:
````
$ knife 
/home/user/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/chef-vault-1.2.3/lib/chef/knife/EncryptCert.rb:23:in `<class:EncryptCert>': uninitialized constant EncryptCert::ChefVault (NameError)
  from /home/user/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/chef-vault-1.2.3/lib/chef/knife/EncryptCert.rb:18:in `<top (required)>'
  from /home/user/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/chef-11.4.4/lib/chef/knife/core/subc
ommand_loader.rb:37:in `load'
  from /home/user/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/chef-11.4.4/lib/chef/knife/core/subcommand_loader.rb:37:in `block in load_commands'
  from /home/user/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/chef-11.4.4/lib/chef/knife/core/subcommand_loader.rb:37:in `each'
  from /home/user/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/chef-11.4.4/lib/chef/knife/core/subcommand_loader.rb:37:in `load_commands'
  from /home/user/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/chef-11.4.4/lib/chef/knife.rb:119:in `load_commands'
  from /home/user/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/chef-11.4.4/lib/chef/knife.rb:167:in `run'
  from /home/user/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/chef-11.4.4/lib/chef/application/knife.rb:123:in `run'
  from /home/user/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/chef-11.4.4/bin/knife:25:in `<top (required)>'
  from /home/user/.rbenv/versions/1.9.3-p429/bin/knife:23:in `load'

````

So I moved the include into the lazily loaded `dep` method block. 

P.S. Sorry for the whitespace changes my editor is tuned to destroy empty whitespace at the end of lines :D
`?w=1` takes care of it