Avoid using echo -n anywhere

`echo -n` is non-portable. The POSIX specification says:

    Conforming applications that wish to do prompting without <newline>
    characters or that could possibly be expecting to echo a -n, should
    use the printf utility derived from the Ninth Edition system.

Since all of the affected shell scripts use a POSIX shell shebang,
replace `echo -n` invocations with printf.

Signed-off-by: Lukas Fleischer <git@cryptocrack.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/subtree/git-subtree.sh

@@ -311,7 +311,7 @@ copy_commit()
 			GIT_COMMITTER_NAME \
 			GIT_COMMITTER_EMAIL \
 			GIT_COMMITTER_DATE
-		(echo -n "$annotate"; cat ) |
+		(printf "%s" "$annotate"; cat ) |
 		git commit-tree "$2" $3  # reads the rest of stdin
 	) || die "Can't copy commit $1"
 }