Trivial cleanup, but differentiates from the general obj_list used
elsewhere.

When an open() call fails, we don't inject an error, but we didn't
apply this logic when replaying a failpath, with strange results.

This is useful for seeing where failures cause us to run slowly
(ie. we continue for a long time before terminating).

We have to be consistent with the caller, so turn on 64 bit offsets if
available for both the caller and us.

As pointed out by Christian Thaeter, it has bitrotted.

Now valgrind children report failures, this one test fails.

This is the CCAN Way.  Plus, eliminates a compile warning here.

As per the SAMBA version.

Now we can mark test files as FAIL and not be bothered by them.

For example, valgrind can't handle some things, so we may need to
switch it off, but we don't want to do that for every test.

So, start a standard format for per-file restrictions, eg:

    Ccanlint: tests_pass_valgrind test/foo.c:FAIL

For the moment, only tests_pass_valgrind takes options, so it has to
change: we now have a helper which returns the array of options
applicable to a given file.

Valgrind notes that our child processes leak memory.

We turned on --child-silent-after-fork=yes, because the output
confused our dumb parser.  Now we split output by prefix ("==<pid>==")
and then we can sort out the leaks from the errors.

This means we find more errors.... next patch!

Our own dogfood, and it's yummy!

Simplifies future patches.

Memory leak in tests revealed bug in jmap_free.  Also, out-by-one
error.

We can only test the featureless tests, once we've built them!

layout.c's TDB creation functions were incorrect in case of a hash
collision, causing occasional failure.  Make it always use the
(previously-failing) seed value, and fix it.

It's just a header, I don't care what's done with it.

NOTE: btree was originally copyright 2010, and has not been
touched by me since then.  I don't know if changing the license
to something more permissive requires updating the copyright year
or not.

NOTE: block_pool was originally copyright 2009, and has not been
touched by me since then.  I don't know if changing the license
to something more permissive requires updating the copyright year
or not.

No point checking malloc failure in usage(), since we don't elsewhere.
We get 100% coverage with -O (due to code elimination) or 64 bit.