[poppler] poppler::ustring encoding issue

[Jeroen Ooms]

Thanks everyone for the work on this issue, really appreciate the
input. Also excited about mpsuzuki's suggestion to include font data
with the text_list, this will be super helpful.

I have updated and cleaned my example code a little bit to make it
easier to test these issues. The updated test program and a small pdf
file (with expected output) are now here:
https://github.com/jeroen/popplertest . This makes it easier to update
the example for new features/issues.

It seems there are at least 3 places where encoding is not behaving as
expected in 0.63: in the text_list and info_keys and toc. I think
mpsuzuki's patch addresses these problems.