UTF-8: introduce i18n.logoutputencoding.

It is plausible for somebody to want to view the commit log in a
different encoding from i18n.commitencoding -- the project's
policy may be UTF-8 and the user may be using a commit message
hook to run iconv to conform to that policy (and either not have
i18n.commitencoding to default to UTF-8 or have it explicitly
set to UTF-8).  Even then, Latin-1 may be more convenient for
the usual pager and the terminal the user uses.

The new variable i18n.logoutputencoding is used in preference to
i18n.commitencoding to decide what encoding to recode the log
output in when git-log and friends formats the commit log message.

Signed-off-by: Junio C Hamano <junkio@cox.net>

environment.c

@@ -18,7 +18,8 @@ int prefer_symlink_refs;
 int log_all_ref_updates;
 int warn_ambiguous_refs = 1;
 int repository_format_version;
-char git_commit_encoding[MAX_ENCODING_LENGTH] = "utf-8";
+char *git_commit_encoding;
+char *git_log_output_encoding;
 int shared_repository = PERM_UMASK;
 const char *apply_default_whitespace;
 int zlib_compression_level = Z_DEFAULT_COMPRESSION;