replace deprecated default value retrieval on PostgreSQL

lib/Doctrine/DBAL/Platforms/PostgreSqlPlatform.php

@@ -379,7 +379,7 @@ class PostgreSqlPlatform extends AbstractPlatform
                         AND pg_index.indkey[0] = a.attnum
                         AND pg_index.indisprimary = 't'
                     ) AS pri,
-                    (SELECT pg_attrdef.adsrc
+                    (SELECT pg_get_expr(adbin, adrelid)
                      FROM pg_attrdef
                      WHERE c.oid = pg_attrdef.adrelid
                         AND pg_attrdef.adnum=a.attnum
@@ -485,7 +485,7 @@ class PostgreSqlPlatform extends AbstractPlatform
                 $sql[] = 'ALTER TABLE ' . $diff->getName()->getQuotedName($this) . ' ' . $query;
             }
 
-            if ($columnDiff->hasChanged('default')) {
+            if ($columnDiff->hasChanged('default') || $columnDiff->hasChanged('type')) {
                 $defaultClause = null === $column->getDefault()
                     ? ' DROP DEFAULT'
                     : ' SET' . $this->getDefaultValueDeclarationSQL($column->toArray());