[cgiapp] PATCH: better error handling and auto-flushing for Stream plugin

[Mark Stosberg]

Attached is a patch for CGI::Application::Plugin::Stream. It proposes
the following changes, and includes full test and doc updates. 

  * Turn on local auto-flushing automatically. (Mark Stosberg)
  * New stream() method provides access to $@ if there is a problem,
    and will invoke error_mode() automatically if no other error
    handing is installed. (Mark Stosberg).

Before making a new release of it, I would also consider replacing
File::MMagic with an alternative, because File::MMagic is full of bugs
and not maintained. I currently don't have a strong alternative
recommendation, but perhaps you do. 

I've inquired in PerlMonks about using File::MimeInfo instead:
http://www.perlmonks.org/?node_id=693367

   Mark
   (who is back from YAPC with renewed energy for CGI::App hacking).