parse-options: properly align continued usage output

Some commands such as "git stash" emit continued options output with e.g. "git stash -h", because usage_with_options_internal() prefixes with its own whitespace the resulting output wasn't properly aligned. Let's account for the added whitespace, which properly aligns the output. The "git stash" command has usage output with a N_() translation that legitimately stretches across multiple lines; N_("git stash [push [-p|--patch] [-k|--[no-]keep-index] [-q|--quiet]\n" " [-u|--include-untracked] [-a|--all] [-m|--message <message>]\n" [...] We'd like to have that output aligned with the length of the initial "git stash " output, but since usage_with_options_internal() adds its own whitespace prefixing we fell short, before this change we'd emit: $ git stash -h usage: git stash list [<options>] or: git stash show [<options>] [<stash>] [...] or: git stash [push [-p|--patch] [-k|--[no-]keep-index] [-q|--quiet] [-u|--include-untracked] [-a|--all] [-m|--message <message>] [...] Now we'll properly emit aligned output. I.e. the last four lines above will instead be (a whitespace-only change to the above): [...] or: git stash [push [-p|--patch] [-k|--[no-]keep-index] [-q|--quiet] [-u|--include-untracked] [-a|--all] [-m|--message <message>] [...] We could also go for an approach where we have the caller support no padding of their own, i.e. (same as the first example, except for the padding on the second line): N_("git stash [push [-p|--patch] [-k|--[no-]keep-index] [-q|--quiet]\n" "[-u|--include-untracked] [-a|--all] [-m|--message <message>]\n" [...] But to do that we'll need to find the length of "git stash". We can discover that from the "cmd" in the "struct cmd_struct", but there might be cases with sub-commands or "git" itself taking arguments that would make that non-trivial. Even if it were I still think this approach is better, because this way we'll get the same legible alignment in the C code. The fact that usage_with_options_internal() is adding its own prefix padding is an implementation detail that callers shouldn't need to worry about. Implementation notes: We could skip the string_list_split() with a strchr(str, '\n') check, but we'd then need to duplicate our state machine for strings that do and don't contain a "\n". It's simpler to just always split into a "struct string_list", even though the common case is that that "struct string_list" will contain only one element. This is not performance-sensitive code. This change is relatively more complex since I've accounted for making it future-proof for RTL translation support. Later in usage_with_options_internal() we have some existing padding code dating back to d7a38c54a6c (parse-options: be able to generate usages automatically, 2007-10-15) which isn't RTL-safe, but that code would be easy to fix. Let's not introduce new RTL translation problems here. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>