bug#25322: preview-latex coding system problem with Japanese LaTeX

[Ikumi Keita]

Hi Mosè and all,

>> I only read the patch, didn't actually try it, but I'm confident you
>> did it ;-)  I didn't see anything clearly wrong.  I have only a
>> request: do you think it's possible to add a test for this fix?

> OK, I'll try.  Maybe it takes a week or so.  I'll also wait for possible
> comments from others to arrive during that.

I wrote a suite of ERT files and commited them with the patches, since I
heard no objections during the span.  I also commited the patch in my
previous message to make preview-latex to work with xemacs on w32
system.

Since it was too difficult for me to write a full automated test which
can complete entirely in batch mode because the functionality of
preview-latex depends how images scattered on the buffer "look" like to
human eyes, some of the tests are marked to be skipped in batch mode.
Such tests requires manual execution instead.

If someone finds difficulties with this commit, feel free to ask me.

Best regards,
Ikumi Keita