Formatting.
Add has_policy<> and remove has_yield<>.

Conflicts:
	luabind/yield_policy.hpp
Don't construct T* const& types for attribute access.
Remove instance_holder dependency on class_rep.

Conflicts:
	luabind/detail/class_rep.hpp
	luabind/detail/instance_holder.hpp
	luabind/detail/object_rep.hpp

(Christian N.: Also clean up detail/class_rep.hpp #includes.)
Allow overriding virtual functions per instance.

This changes the way virtual function overrides are fetched so that it
is possible to override them directly on an instance, rather than
creating a derived class in Lua:

  x = X()
  x.virtual_function = function(self) ... end

Conflicts:
	src/wrapper_base.cpp
docs: fix typo, "base" should be "derived".
Fix LUABIND_ERROR_CHECKING conversion bug.

Conflicts:
	luabind/detail/call_function.hpp
	luabind/detail/call_member.hpp
Add policy to suppress automatic attribute dependency.

Can be used with def_readwrite/def_readonly to suppress the default
dependency policy. This is useful if the attribute is a
pointer/reference that isn't owned by the enclosing class.

Conflicts:
	luabind/class.hpp
	test/test_attributes.cpp
Teach adopt() to hold the adopted pointer in custom pointer type.

Conflicts:
	luabind/adopt_policy.hpp