test_requires

Howdy,

I'm working on a series of modules for a client. We developers need a  
bunch of test modules, but OPS will want to just install the module  
without running tests.

I've been putting the test module requirements into `build_requires`:

     configure_requires => { 'Module::Build' => '0.2701' },
     build_requires     => {
         'Module::Build'        => '0.2701',
         'Test::File'           => '1.08',
         'Test::File::Contents' => 0,
         'Test::MockModule'     => '0.04',
         'Test::More'           => '0.17',
         'Test::NoWarnings'     => 0,
         'Test::Output'         => 0,
     },

But this will be annoying for OPS, since it's not the build that  
requires those Test:: modules; it's testing.

So, can we finally have a `test_requires` option? If so, I'd be happy  
to dig up some tuits and send in a patch.

Thanks,

David