synchronize init_connection (all public methods doing newConnection sync)

Author: kares

src/java/arjdbc/jdbc/RubyJdbcConnection.java

@@ -444,7 +444,7 @@ public IRubyObject set_connection_factory(final ThreadContext context, final IRu
      * @return connection
      */
     @JRubyMethod(name = "init_connection")
-    public IRubyObject init_connection(final ThreadContext context) throws SQLException {
+    public synchronized IRubyObject init_connection(final ThreadContext context) throws SQLException {
         final IRubyObject jdbcConnection = setConnection( newConnection() );
         final IRubyObject adapter = callMethod("adapter"); // self.adapter
         if ( ! adapter.isNil() ) {