Fixing line_pos_iterator column numbering bug and get_current_line bug.

This is cleaned up version of https://github.com/boostorg/spirit/pull/39.

This pull request fixes following bugs.
- line_pos_iterator's column numbering bug.
- line_pos_iterator's get_current_line bug.

And add regression test for line_pos_iterator.
Thank you.I changed from all BOOST_TEST to BOOST_TEST_EQ.