Make PostgreSQL specs pass when PostgreSQL is not built with libxml s…

…upport

This seems an uncommon way to build PostgreSQL, considering that
nobody has reported this issue, but since libxml is not required
to build PostgreSQL, Sequel's specs should work without it.

spec/adapters/postgres_spec.rb

@@ -3214,7 +3214,18 @@ def c.get_last_result; end
       column :o, 'oidvector[]'
     end
     @tp.call.must_equal [:xml_array, :money_array, :bit_array, :varbit_array, :uuid_array, :xid_array, :cid_array, :name_array, :oidvector_array]
-    @ds.insert(Sequel.pg_array(['<a></a>'], :xml),
+
+    begin
+      @db.transaction(:rollback=>:always) do
+        @ds.insert(:x=>Sequel.pg_array(['<a></a>'], :xml))
+      end
+    rescue Sequel::DatabaseError
+    else
+      xml_insert_value = Sequel.pg_array(['<a></a>'], :xml)
+      xml_expected_value = ['<a></a>']
+    end
+
+    @ds.insert(xml_insert_value,
                Sequel.pg_array(['1'], :money),
                Sequel.pg_array(['1'], :bit),
                Sequel.pg_array(['10'], :varbit),
@@ -3230,10 +3241,12 @@ def c.get_last_result; end
     m.class.must_equal(Sequel::Postgres::PGArray)
     m.to_a.must_be_kind_of(Array)
     m.first.must_be_kind_of(String)
-    r.must_be(:==, :x=>['<a></a>'], :b=>['1'], :vb=>['10'], :u=>['c0f24910-39e7-11e4-916c-0800200c9a66'], :xi=>['12'], :c=>['12'], :n=>['N'], :o=>['1 2'])
-    rs.first.values.each{|v| v.class.must_equal(Sequel::Postgres::PGArray)}
-    rs.first.values.each{|v| v.to_a.must_be_kind_of(Array)}
+    r.must_be(:==, :x=>xml_expected_value, :b=>['1'], :vb=>['10'], :u=>['c0f24910-39e7-11e4-916c-0800200c9a66'], :xi=>['12'], :c=>['12'], :n=>['N'], :o=>['1 2'])
+    x = r.delete(:x)
+    r.values.each{|v| v.class.must_equal(Sequel::Postgres::PGArray)}
+    r.values.each{|v| v.to_a.must_be_kind_of(Array)}
     r[:m] = m
+    r[:x] = x
     @ds.delete
     @ds.insert(r)
     @ds.all.must_equal rs