bug#23730: 24.5; format removes text properties

[ynyaaa]

Eli Zaretskii <eliz@gnu.org> writes:

>The documentation only promises that the characters
>_other_ than the format specifier are copied with their properties,

Text properties after the format spericifier are copied
with wrong positions.

(format (concat (propertize "%2d" 'x 'X)
                (propertize "a" 'a 'A)
                (propertize "b" 'b 'B))
        1)
=>#(" 1ab" 0 1 (a A) 1 2 (b B))