(bug 66345) solve unicode error in html2unicode

unichr() isn't defined for values >= 0x10000 in python 2
(I guess in py3 it is, but there are remaining problems on Windows
for py < 3.4)
and raises a ValueError with that remark "(narrow Python build)".

Now unicode char is created as '\Uxxxxxxxx' literal.

Change-Id: I7a38aae7a19079e7cdf93d6cc6922b2214558973