[Commits] [wesnoth/wesnoth] c0c6f7: fix compilation

[GitHub]

  Branch: refs/heads/master
  Home:   https://github.com/wesnoth/wesnoth
  Commit: c0c6f71725ad3e0bcbf9dc0632c2ed767b4723a9
      https://github.com/wesnoth/wesnoth/commit/c0c6f71725ad3e0bcbf9dc0632c2ed767b4723a9
  Author: gfgtdf <tischpapier at gmail.com>
  Date:   2015-02-12 (Thu, 12 Feb 2015)

  Changed paths:
    M src/scripting/game_lua_kernel.cpp

  Log Message:
  -----------
  fix compilation

msvc liked the previous code but travis said:
usr/include/boost/optional/optional.hpp:526:5: candidate constructor not
      viable: no known conversion from 'const config::attribute_value::yes_no'
      to 'argument_type' (aka 'const bool &') for 1st argument.
    optional ( argument_type val ) : base(val) {}
I hope travis likes this version.