Catch annotation sequences that don't end with newline

ticket:265
for some unknown reason if the last sequence in an annotation file
wasn't terminated by a new line, spirit ended up duplicating the
last character. Needless to say this meant that it wouldn't always
align properly.

I installed a hack into push_back_seq::operator() that checks for
this condition and removes the duplicated character if the bug was
triggered.

Needless to say if spirit (or my grammar) gets fixed and this bug goes
away the hack will need to be removed. I think the sequence equality
tessts in test_sequence::sequence_no_trailing_newline should trip if
the last character doesn't get duplicated.

Also I didn't test what happens if a location based sequence doesn't
end with a newline.