Commit 29c75ddd "json-streamer: limit the maximum recursion depth and
maximum token count" attempts to guard against excessive heap usage by
limiting total token size (it says "token count", but that's a lie).

Total token size is a rather imprecise predictor of heap usage: many
small tokens use more space than few large tokens with the same input
size, because there's a constant per-token overhead: 37 bytes on my
system.

Tighten this up: limit the token count to 2Mi.  Chosen to roughly
match the 64MiB total token size limit.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Message-Id: <1448486613-17634-13-git-send-email-armbru@redhat.com>