boost::mpl: semi-variadic bind<>

As it is not obvious to me at this time how to make a truly variadic
bind<>, only bind::apply<> is made variadic, while bind<> itself is
manually instantiated for up to 5 parameters (same as original mpl).

At any rate, 3 parameter bind requires specialized partial specializations
for if_ and eval_if.

Signed-off-by: Alex Dubov <oakad@yahoo.com>