title: ERROR: data type inet has no default operator class for access method "gist"
body: <p>Using PostgreSQL version <code>9.4.5</code>, I have a table that contains an <code>INET</code> column.
  In that column I have a <code>gist</code> index</p>
  
  <pre><code>CREATE TABLE ipv4_prefix (
      id uuid DEFAULT public.uuid_generate_v4() NOT NULL,
      prefix inet NOT NULL,
      CONSTRAINT ck_ipv4_prefix_valid_ipv4 CHECK ((family(prefix) = 4))
  );
  ALTER TABLE ONLY ipv4_prefix ADD CONSTRAINT pk_ipv4_prefix PRIMARY KEY (id);
  CREATE INDEX ipv4_prefix_gist_index ON ipv4_prefix USING gist (prefix inet_ops);
  </code></pre>
  
  <p>This all seems to work:</p>
  
  <pre><code>mimir=# \d ipv4_prefix
                Table "ipv4_prefix"
   Column | Type |              Modifiers              
  --------+------+-------------------------------------
   id     | uuid | not null default uuid_generate_v4()
   prefix | inet | not null
  Indexes:
      "pk_ipv4_prefix" PRIMARY KEY, btree (id)
      "ipv4_prefix_gist_index" gist (prefix inet_ops)
  Check constraints:
      "ck_ipv4_prefix_valid_ipv4" CHECK (family(prefix) = 4)
  </code></pre>
  
  <p>However, when I try to add an <code>EXCLUDE</code> constraint:</p>
  
  <pre><code>ALTER TABLE ipv6_prefix ADD CONSTRAINT ipv6_prefix_exclude_constraint EXCLUDE USING gist (prefix WITH &amp;&amp;);
  </code></pre>
  
  <p>I get the following error:</p>
  
  <pre><code>ERROR:  data type inet has no default operator class for access method "gist"
  HINT:  You must specify an operator class for the index or define a default operator class for the data type.
  </code></pre>