redefine String#+

redefine_string_plus

$ irb
ruby-1.8.7-p352 :001 > str = 'a'
 => "a" 
ruby-1.8.7-p352 :002 > str + 'b'
 => "ab" 
ruby-1.8.7-p352 :003 > p str                                                          
"a"
 => nil 
ruby-1.8.7-p352 :004 > class String
ruby-1.8.7-p352 :005?>   def +(other)                                                 
ruby-1.8.7-p352 :006?>     self.concat(other)
ruby-1.8.7-p352 :007?>   end
ruby-1.8.7-p352 :008?> end
 => nil 
ruby-1.8.7-p352 :009 > str2 = 'a'
 => "a" 
ruby-1.8.7-p352 :010 > str2 + 'b'
 => "ab" 
ruby-1.8.7-p352 :011 > p str2                                                         
"ab"
 => nil