rfc822: beef up _info example.

Now it's a useful little command line utility, with tests.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
rfc822: fix sigaction test, wean off ccan-specific talloc_set_allocator()

The first ok() line was actually failing, because sigaction returns 0
on success, but because the program exit(0) out the abort handler,
that wasn't being seen.

So remove tap and just abort and assert our way through the test,
which I think is clearer.

We use macros to mug the talloc entry points, since talloc_set_allocator()
is not in mainline talloc.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
tal/talloc: new module for backending tal onto talloc.

David Gibson points out that a project may already be using talloc, so
this gives a simple adapter if one module uses tal.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
ccanlint: ignore "unused" non-ccan dependencies.

We can't really tell if non-ccan dependencies are used, so don't try.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
tal/str: use tal/talloc backend #ifdef TAL_USE_TALLOC.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
rfc822: switch to ccan/tal.

We use TAL_USE_TALLOC to use libtalloc as the backend: you can test that with
ccanlint --compiler="cc -DTAL_USE_TALLOC".

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Merge branch 'rfc822'