Don't allow NULL descs, and put them in macro.  Users can use "", but make
sure it's explicit, not an accidental omission.
Use errx() instead of assert() for API usage errors.
Rename opt_flags to opt_type.

I still don't like the duplication, but it's clearer and not much longer.

longidx is not updated in this case.  We should open-code option parsing.

This is more explicit than separate short and long (great for grep!) and
simpler.

This includes renaming ATTRIBUTE_UNLIKELY_FUNCTION to ATTRIBUTE_COLD,
and removing unlikely_func macro from ccan/likely.

Valgrind was giving a spurious error.

We were getting occasional failures: if all values are the same it's a 1-line
graph and there's no "|" anywhere.

Currently they sit in each module.

Macro packages do this.

This is a precursor to doing something useful with them.

As per-tdb's tools.

We want it to complain if it's wrong...

That way we match our comment about optimal tally_new() arg matching histogram height.

Including pretty graphs!

Not as trivial as you might think, with overflow and underflow.

This flag to tdb_open/tdb_open_ex effects creation of a new database:
1) Uses the Jenkins lookup3 hash instead of the old gdbm hash if none is
   specified,
2) Places a non-zero field in header->rwlocks, so older versions of TDB will
   refuse to open it.

This means that the caller (ie Samba) can set this flag to safely
change the hash function.  Versions of TDB from this one on will either
use the correct hash or refuse to open (if a different hash is specified).
Older TDB versions will see the nonzero rwlocks field and refuse to open 
it under any conditions.

If the caller to tdb_open_ex() doesn't specify a hash, and tdb_old_hash
doesn't match, try tdb_jenkins_hash.

This makes life simpler, especially with the upcoming TDB_INCOMPATIBLE_HASH
flag.

This is a better hash than the default: shipping it with tdb makes it easy
for callers to use it as the hash by passing it to tdb_open_ex().