Fixed small bugs in several .po files, enabling these translations to

Fixed small bugs in several .po files, enabling these translations to
be used.  They all probably need more work from the translation team.
I don't speak any of these languages, but I did some spot checks
either from my own knowledge or using Google Translate, and they
generally look sane.

- Several files were in utf8 but needed to be marked as such (that is,
  "CHARSET" changed to "UTF-8").  Affected es.po, it.po, ru.po, vi.po,
  zh_CN.po, zh_TW.po.

- it.po was missing a \n at the end of one translation.

- ru.po had unescaped double-quote marks in one translation.

- vi.po needed to be normalized to Unicode normalization form C.  With
  this fix, more characters display correctly, though at least one is
  still missing in the X core fonts that xboard is able to use.
  See http://vietunicode.sourceforge.net/ for more about Vietnamese.

- zh_HK.po was written in big5 and then utf8-encoded on top of that,
  making it unusable.  I stripped off the spurious utf8 encoding and
  then used recode to convert the file to Unicode properly encoded as
  utf8.

Unfortunately, I wasn't able to test any of the Chinese translations,
as I haven't been able to get XCreateFontSet to work in Chinese
locales with any of the fonts I have installed, even after adding the
Ubuntu language support packages for both simplified and traditional
Chinese.  I did spot check a bunch of the translations using Google
Translate.

I've checked in a couple of tiny Perl scripts that I used to do part
of the fixups on vi.po and zh_HK.po in case we need them again.