Options can be used interchangeably with Strings

We want to be able to use Option objects in place of strings and have
this be transparent. Defining to_str means that methods like
Kernel#system and Kernel#exec will be able to perform an implicit
conversion.

Library/Homebrew/formula_support.rb

@@ -172,6 +172,11 @@ class Option
     @flag = '--'+name.to_s
   end
 
+  def to_s
+    flag
+  end
+  alias_method :to_str, :to_s
+
   def eql?(other)
     @name == other.name
   end