Update www/ruby-rack to 1.2.1.

Update www/ruby-rack to 1.2.1.

* Use lang/ruby/gem.mk instead of misc/rubygems/rubygem.mk.
* Add LICENSE.
* Remove default value of GEM_BUILD.

== Changes

* June 13th, 2010: Tenth public release 1.2.0.
  * Removed Camping adapter: Camping 2.0 supports Rack as-is
  * Removed parsing of quoted values
  * Add Request.trace? and Request.options?
  * Add mime-type for .webm and .htc
  * Fix HTTP_X_FORWARDED_FOR
  * Various multipart fixes
  * Switch test suite to bacon

* January 3rd, 2009: Ninth public release 1.1.0.
  * Moved Auth::OpenID to rack-contrib.
  * SPEC change that relaxes Lint slightly to allow subclasses of the
    required types
  * SPEC change to document rack.input binary mode in greator detail
  * SPEC define optional rack.logger specification
  * File servers support X-Cascade header
  * Imported Config middleware
  * Imported ETag middleware
  * Imported Runtime middleware
  * Imported Sendfile middleware
  * New Logger and NullLogger middlewares
  * Added mime type for .ogv and .manifest.
  * Don't squeeze PATH_INFO slashes
  * Use Content-Type to determine POST params parsing
  * Update Rack::Utils::HTTP_STATUS_CODES hash
  * Add status code lookup utility
  * Response should call #to_i on the status
  * Add Request#user_agent
  * Request#host knows about forwared host
  * Return an empty string for Request#host if HTTP_HOST and
    SERVER_NAME are both missing
  * Allow MockRequest to accept hash params
  * Optimizations to HeaderHash
  * Refactored rackup into Rack::Server
  * Added Utils.build_nested_query to complement Utils.parse_nested_query
  * Added Utils::Multipart.build_multipart to complement
    Utils::Multipart.parse_multipart
  * Extracted set and delete cookie helpers into Utils so they can be
    used outside Response
  * Extract parse_query and parse_multipart in Request so subclasses
    can change their behavior
  * Enforce binary encoding in RewindableInput
  * Set correct external_encoding for handlers that don't use RewindableInput