…144)

* Extend __has_include grammar for complex conditional expressions

The logic handling __has_include erroneously assumed it would always
be the last expression on a line. This code fixes that by extending
the grammar to only consume the __has_include() itself, and count
parentheses as necessary to find the correct input range.

Also add some unit tests to cover the error in the future.

* While I'm at it, a couple of small cleanups

1) Remove unneeded header
2) The wrong BOOST_SPIRIT_DEBUG_TRACE_RULE was commented out