utf8.c: partially update to version 6.3

Unicode 6.3 defines more code points as combining or accents.  For
example, the character "ö" could be expressed as an "o" followed by
U+0308 COMBINING DIARESIS (aka umlaut, double-dot-above).  We should
consider that such a sequence of two codepoints occupies one display
column for the alignment purposes, and for that, git_wcwidth()
should return 0 for them.  Affected codepoints are:

    U+0358..U+035C
    U+0487
    U+05A2, U+05BA, U+05C5, U+05C7
    U+0604, U+0616..U+061A, U+0659..U+065F

Earlier unicode standards had defined these as "reserved".

Only the range 0..U+07FF has been checked to see which codepoints
need to be marked as 0-width while preparing for this commit; more
updates may be needed.

Signed-off-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>