bugfix: fix broken time_buf paddings for git-blame

When `git blame` shows date field in a fixed width (as long as
blame_date_width characters), if time_str shorter than that, add spaces
for padding.  But there are two bugs in the following codes:

        memcpy(time_buf, time_str, time_len);
        memset(time_buf + time_len, ' ', blame_date_width - time_len);

1. The type of blame_date_width is size_t (unsigned int).  If time_len
   is greater than blame_ate_width, "blame_date_width - time_len" will
   never be a negative number, but a really big positive number, and
   will cause memory overwrite.

   This bug can be triggered if either l10n message for function
   show_date_relative() in date.c is longer then 30 charcters, then
   `git blame --date relative` may fail.

2. When show blame information with relative time, the UTF-8 characters
   in time_str will break the alignment of columns after the date field.
   This is because the time_buf padding with spaces should have a
   constant display width, not a fixed strlen size.  So we should call
   utf8_strwidth() instead of strlen() for calibration.

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
blame: use different blame_date_width for different locale

When show date in relative date format for `git blame`, the max display
width of datetime is set as the length of the string "Thu Oct 19
16:00:04 2006 -0700" (30 characters long).  But actually the max width
for C locale is only 22 (the length of string "x years, xx months ago").
And for other locale, it maybe smaller.  E.g. For Chinese locale, only
needs 16-character width.

Set blame_date_width as the display width of _("4 years, 11 months
ago"), so that translators can make the choice.

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
l10n: git.pot: v2.0.0 round 1 (45 new, 28 removed)

Generate po/git.pot from v2.0.0-rc0 for git v2.0.0 l10n round 1.

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
l10n: zh_CN.po: translate 45 new messages (2228t0f0u)

Translations for git v2.0.0-rc0.  Also correct translatioins on relative
date in date.c with help from Brian Gesiak ($gmane/246390).

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
l10n: blame_date_width for Chinese

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>