Add missing includes

[ashtum]

No description provided.

[pdimov]

It's hard to say what's the history here.

I suppose this dates from the days when including <boost/bind.hpp> made _1 et al available in the global namespace, which later conflicted with using namespace std::placeholders; which also made _1 available.

So I assume people who were defining BOOST_BIND_NO_PLACEHOLDERS did that in order to be able to use using namespace std::placeholders; in their code. But doing so broke parser.hpp.

This problem will not occur today, because <boost/bind/bind.hpp> leaves the placeholders defined in namespace boost::placeholders, avoiding the conflict. But for backward compatibility, we may want to still support the configuration with BOOST_BIND_NO_PLACEHOLDERS defined.

So adding this include is probably correct, but we need a test that shows why.

[pdimov]

As a general rule, every change that does not immediately fix a test failure needs to follow the procedure of: first commit adds a test that fails without the change, second commit adds the change that fixes the test failure.

[pdimov]

Would you please be able to extract the new test into a separate PR? I'd like to merge the original contribution (#101) as a form of giving credit on top of it.

[ashtum]

Then this PR is waiting for #100 response.