git-svn: Fix time zone in --localtime

git-svn: Fix time zone in --localtime

Use numerical form of time zone to replace alphabetic time zone
abbreviation generated by "%Z". "%Z" is not portable and contain
ambiguity for many areas. For example, CST could be "Central
Standard Time" (GMT-0600) and "China Standard Time" (GMT+0800).
Alphabetic time zone abbreviation is meant for human readability,
not for specifying a time zone for machines.

Failed case can be illustrated like this in linux shell:
  > echo $TZ
  Asia/Taipei
  > date +%Z
  CST
  > env TZ=`date +%Z` date
  Mon Dec 19 06:03:04 CST 2011
  > date
  Mon Dec 19 14:03:04 CST 2011

[ew: fixed bad package reference inside Git::SVN::Log]

Signed-off-by: Wei-Yin Chen (陳威尹) <chen.weiyin@gmail.com>
Acked-by: Eric Wong <normalperson@yhbt.net>