apply: avoid using fixed-size buffer in write_out_one_reject()

apply: avoid using fixed-size buffer in write_out_one_reject()

On some systems PATH_MAX is not a hard limit.  Support longer paths by
building them on the heap instead of using static buffers.

Take care to work around (arguably buggy) implementations of free(3)
that change errno by calling it only after using the errno value.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>