completion: make sed command that generates config-list.h portable.

completion: make sed command that generates config-list.h portable.

The OpenBSD 'sed' command does not support '\n' to represent newlines in
sed expressions. This leads to the follow compiler error:

    In file included from builtin/help.c:15:
    ./config-list.h:282:18: error: use of undeclared identifier 'n'
            "gitcvs.dbUser",n       "gitcvs.dbPass",
                            ^
    1 error generated.
    gmake: *** [Makefile:2821: builtin/help.o] Error 1

We can fix this by documenting related configuration variables
one-per-line instead of listing them separated by commas. This allows us
to remove the unportable part of the sed expression in
generate-configlist.sh.

Signed-off-by: Collin Funk <collin.funk1@gmail.com>
Reviewed-by: Jacob Keller <jacob.keller@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>