Bug#253404: debian-installer: The default locale should be seted to "POSIX" after installation

[Tetralet <tetralet@pchome.com.tw>]

Package: debian-installer
Severity: important
Tags: l10n

After the installation,
We find that the locale was seted to: (if Debian was installed in Traditional Chinese)

  LANG=zh_TW
  LC_CTYPE="zh_TW"
  LC_NUMERIC="zh_TW"
  LC_TIME="zh_TW"
  LC_COLLATE="zh_TW"
  LC_MONETARY="zh_TW"
  LC_MESSAGES="zh_TW"
  LC_PAPER="zh_TW"
  LC_NAME="zh_TW"
  LC_ADDRESS="zh_TW"
  LC_TELEPHONE="zh_TW"
  LC_MEASUREMENT="zh_TW"
  LC_IDENTIFICATION="zh_TW"
  LC_ALL=

User's console may not be able to show Traditional Chinese characters correctly,
When some command output Traditional Chinese characters, The outputs will become illegible codes.
It may confuse users.

-- System Information:
Debian Release: 3.0
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'unstable')
Architecture: i386 (i686)
Kernel: Linux 2.6.5-1-686
Locale: LANG=C, LC_CTYPE=zh_TW.Big5