Add specs for Socket::Option.

Add specs for Socket::Option.new, Socket::Option.int,
Socket::Option#int, Socket::Option.linger and
Socket::Option#linger.

These specs have passed with ruby 1.9.3 on linux. Not tested
under Windows.
Add specs for BasicSocket.

Add specs for BasicSocket#getsockopt and #setsockopt.
These specs specify how these methods use Socket::Option.
Add Socket::Option.

* lib/19/socket.rb:
  Make BasicSocket#getsockopt return a Socket::Option instead
  of a string.
  Make BasicSocket#setsockopt accept a Socket::Option as
  uniq parameter.
  Add class Socket::Option

* rakelib/platform.rake:
  Add linger structure used by Socket::Option.

* spec/tags/19/ruby/library/socket/socket/connect_nonblock_tags.txt:
  Bonus: Socket::Option makes this spec pass!
Add a new helper to spec.

pack_int helper added.
This new helper is used in library/socket/basicsocket/setsockopt
spec.
Merge remote-tracking branch 'sdaubert/socketoption'