i18n: am: mark more strings for translation

i18n: am: mark more strings for translation

Mark strings in 'git-am.sh' for translation. In the last chunk,
change '$1' to '-b/--binary', as it is not worth turning this
message to "The %s option has been..." and using printf on it.

Also reduce one indentation level for one gettextln clause introduced
in commit de88c1c.

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
Reviewed-by: Stefano Lattarini <stefano.lattarini@gmail.com>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>