libc - fix handling of temporary file used by hash(3)

libc - fix handling of temporary file used by hash(3)

This fixes applications using DB_HASH, such as tsort, to unexpectedly
try to open a temporary file in the current directory and fail if it
has no write permission there.

Obtained from FreeBSD, r190485, by delphij:

  db/btree/bt_open.c: check return value of snprintf() and return value
  if the result is truncated.

  db/hash/hash_page.c: use the same way to create temporary file as
  bt_open.c; check snprintf() return value.

  Obtained from:  OpenBSD