git-gui/gitk: Do not use a Cygwin-specific kill flag on Windows

Windows does not necessarily mean Cygwin, it could also be MSYS. The
latter ships with a version of "kill" that does not understand "-f". In
msysgit this was addressed shipping Cygwin's version of kill.

Properly fix this by using the stock Windows "taskkill" command instead,
which is available since Windows XP Professional.

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
Merge pull request #239 from sschuberth/taskkill

git-gui/gitk: Do not use a Cygwin-specific kill flag on Windows
Enable Python by default on MINGW
Convert charactor encoding to utf-8 on MINGW before git fast-import

System default in Japanese Language version
 * p4: CP932 on Windows
 * msysgit: UTF-8 on Windows(MINGW)
Cosmetic change
Improve conversion of character encoding

- Make use of P4CHARSET environment variable
- Make use of encode method with ignore option
Add URLs to refer to character encodings

 * http://www.perforce.com/perforce/doc.current/user/i18nnotes.txt
 * http://docs.python.org/2.7/library/codecs.html#standard-encodings
Improve conversion of character encoding when p4 submit

- Convert character encoding of logMessage to P4CHARSET or to a encoding
  from user preferences, appropriately
- Separate p4char2encode hash from tounicode function, accordingly
- Use the Codec instead of Aliases in Python Standard Encodings

https://docs.python.org/2.7/library/codecs.html#standard-encodings
- Distinguish decoded data and data
- Make debug print conditionally
Decode with utf_8 if core.quotepath is true (default)

  http://qiita.com/kumazo@github/items/2169e1ee7be278f82b94#1-4

  git status や git diff などで表示される日本語ファイル名は "\nnn" にエスケープされてしまって読めない。
  以下の設定を追加することで日本語ファイル名が表示されるようになる。

  $ git config --global core.quotepath false