Rack rack

FCGI will use pure ruby if:

1. FCGI_PURE_RUBY is set to true before the fcgi library is loaded
   
2. The C version of FCGI doesn't load (lib not found or the like)

The class FCGI::Stream does not exist in the pure ruby version of the FCGI module. Rack::Handler::FastCGI tries to override the FCGI::Stream.read() method, but will fails with the following error:

undefined method read' for classFCGI::Stream' (NameError)

My patch checks that the FCGI::Stream class exists, before trying to override the read method. It is committed here:

http://github.com/dmann/rack/commit/c87b7cfdf0f978062acc7d63ebd0a1c...

And it basically amounts to:

+if FCGI.const_defined? "Stream" class FCGI::Stream

 alias _rack_read_without_buffer read
 def read(n, buffer=nil)
   buf = _rack_read_without_buffer n
   buffer.replace(buf.to_s)  if buffer
   buf
 end

end +end

This is also related to the following ticket:

http://rack.lighthouseapp.com/projects/22435-rack/tickets/61