[Catalyst] Why does the installer include the 'xt' directory

[Robert Rothenberg]

We are deploying our Catalyst apps by installing them into local::lib
directories for specific users. (Yes, I know many people prefer to just run
the application as-is from the source tree, but we don't.)

Everything works fine, however, Module::Install::Catalyst installs the 'xt'
directory in lib/perl5/MyApp. Why does it do this, and how does one tell it
not to?