Introduce i18n.commitencoding.

This is to hold what the project-local rule as to the
charset/encoding for the commit log message is.  Lack of it
defaults to utf-8.

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

environment.c

@@ -14,6 +14,7 @@ char git_default_name[MAX_GITNAME];
 int trust_executable_bit = 1;
 int only_use_symrefs = 0;
 int repository_format_version = 0;
+char git_commit_encoding[MAX_ENCODING_LENGTH] = "utf-8";
 
 static char *git_dir, *git_object_dir, *git_index_file, *git_refs_dir,
 	*git_graft_file;