If we need to clean up the children, they didn't exit cleanly.

This takes a bit more care when writing tests, but found a leak in tdb2.

tdb2 has various places where it recovers from failure (eg. falling
back when it can't open /dev/urandom, or allocation for error
logging).  We want to test those paths, but doing so thoroughly causes
cominatorial explosion.

Add FAIL_PROBE for such cases: in this case it goes only 3 more calls
deep.

We trap them, might as well put them in history.  This also makes tracking
open file descriptors more robust.

ie. SIGUSR1 means it timed out.

If children and parents aren't isolated properly (ie. failtest is
buggy) we really want to run gdb on a failing child.  This hack allows that.

open fails in fairly normal cases; don't double execution time for this!

We insist they write the same things to pipes, since we can't "undo" them,
but strictly speaking we don't care if they write different things into
files.

Note: it may indicate a bug if they do...

The idea of saving files as we do writes doesn't work with mmap: this just
saves the entire contents of all open files before forking child, and
restores them afterwards.

Use the same structure we use in the history.

Each function in the history stores a cleanup function, rather than storing
extra structures.  In particular, we save writes and file offsets using
this.

Append a "+" if you want to start forking as normal.

Useful for showing exactly where we inserted failures, and how long each
one took.

Correctly mark which calls we failed.

Catch fcntl, particularly fcntl locks.

If 'localhost' exists in /etc/hosts with a v4 and a v6 address, the hack
which joins two addrinfo entries together is not necessary.  Detect to see
if 'localhost' returned a v6 address, and if so, just return the single
linked list result from getaddrinfo()

(Reworked by Rusty Russell)
Signed-off-by: Sam Vilain <sam@vilain.net>

move daemon-with-notify to daemon_with_notify as dashes aren't allowed in CCAN module names (and ccanlint segfaults on them)

The type checking function does not use its parameter:

    ccan/opt/opt.h: In function ‘_check_is_entry’:
        ccan/opt/opt.h:328:53: warning: unused parameter ‘e’

Annotate the function using UNUSED from compiler.h.  This commit also
adds compiler.h as a dependency for opt.