Mixin that adds a "symbol_column" declaration to a class. After including this module, if ‘frob’ is a string-valued column of table foo, and the definition of Foo in foo.rb declares

   symbol_column :frob

then the following will work:

   my_foo = Foo.new :frob => :frog
   my_foo.frob = :frill

and reading my_foo.frob will likewise return a symbol, not a string. Also, for UI convenience:

   my_foo.frob = 'frill'
   assert_equal :frill, my_foo.frob

will succeed — we apply to_sym going in as well as coming out.