This is a non-POSIX/ISO-C header. It is ok to include this on Linux, but it
is obsolete on BSD; FreeBSD even throws an error if you include it with
__STDC__ defined. Every system should nowadays have malloc() defined in
stdlib.h.
Diff is largely mechanical, replacing malloc.h with stdlib.h where it is not
yet included anyway.
With Aaron's fixes to dtdbcache fixing a potential coredump, the
comment block in the write_db() function regarding tmpnam() no longer
applies, and the tmpnam_buf variable is no longer used.
So, remove them :)
