Increase POLICY_BUF_LEN to 72 to accomodate IPv6 exit policy items.

Fixes bug 9596; bugfix on 0.2.4.7-alpha.
Fix an assert when disabling ORPort with accounting disabled.

The problem was that the server_identity_key_is_set() function could
return true under conditions where we don't really have an identity
key -- specifically, where we used to have one, but we stopped being a
server.

This is a fix for 6979; bugfix on 0.2.2.18-alpha where we added that
assertion to get_server_identity_key().
Merge remote-tracking branch 'public/bug9596' into maint-0.2.4
Merge remote-tracking branch 'origin/maint-0.2.3' into maint-0.2.4