Fixes bug 25276; bugfix not in any released Tor.

Instead, define a maximum size, and enforce it with an assertion.

(When a variable isn't going to be declared extern in the header, we
require that it be static.)

 * FIXES #25271: https://bugs.torproject.org/25271

Add an autoconf test to make sure we won't regret it.

Closes ticket 24484.

Empty versions lists are permitted; empty keywords are not.

Part of the 25249 fix to make rust match the C.

Also correct MAX_VERSIONS_TO_EXPAND to match the C.

NOTE that this patch leads to incorrect behavior: the C code allows
huge ranges; it just doesn't allow votes on them (currently).  For
full compatibility, we'll need to make the rust code store ranges as
ranges natively, possibly using something like the range_map crate.

Still, this patch is smaller than a "proper" fix.

Fixes TROVE-2018-003.

Signed-off-by: David Goulet <dgoulet@torproject.org>

Fixes #25236

Signed-off-by: David Goulet <dgoulet@torproject.org>

Never allow the function to set a bucket value above the allowed circuit
burst.

Closes #25202

Signed-off-by: David Goulet <dgoulet@torproject.org>

We had this safeguard around dos_init() but not when the consensus changes
which can modify consensus parameters and possibly enable the DoS mitigation
even if tor wasn't a public relay.

Fixes #25223

Signed-off-by: David Goulet <dgoulet@torproject.org>