Fix ruby worker with ruby 1.9 & non-latin characters.

Ruby 1.8 works fine, for packed and unpacked strings length is equal:
irb(main):002:0> t = 'Raphaël'
"Rapha\303\253l"
irb(main):003:0> t.size
8
irb(main):004:0> [t].pack('a*').size
8

but not for Ruby 1.9, .size for string means count of characters, not size in bytes:
irb(main):022:0> t = 'Raphaël'
=> "Raphaël"
irb(main):023:0> t.size
=> 7
irb(main):024:0> [t].pack('a*').size
=> 8