srdb1: table_name set to unique constraint in version table

lib/srdb1/schema/version.xml

@@ -10,15 +10,20 @@
     <name>version</name>
     <type db="mysql">&MYSQL_TABLE_TYPE;</type>
 
-    <column id="tn">
+    <column id="table_name">
         <name>table_name</name>
         <type>string</type>
         <size>32</size>
         <natural/>
     </column>
-    <column id="tv">
+    <column id="table_version">
         <name>table_version</name>
         <type>unsigned int</type>
         <default>0</default>
     </column>
+    <index>
+        <name>table_name_idx</name>
+        <colref linkend="table_name"/>
+        <unique/>
+    </index>
 </table>