define variables only where needed, and use NULL to define them, as some places test only for isset and not for content

ChangeLog

@@ -7,6 +7,9 @@ $Source$
 
 2005-11-24 Sebastian Mendel <cybot_tm@users.sourceforge.net>
     * libraries/grab_globals.lib.php: allow scripts to bypass importing vars
+    * libraries/common.lib.php, libraries/export/sql.php: define variables only
+      where needed, and use NULL to define them, as some places test only for
+      isset and not for content
     
 2005-11-25 Marc Delisle  <lem9@users.sourceforge.net>
     * main.php: move server choice into MySQL container

libraries/common.lib.php

@@ -54,9 +54,6 @@ $GLOBALS['PMA_errors'] = array();
 /**
  * Avoids undefined variables
  */
-if (!isset($use_backquotes)) {
-    $use_backquotes   = 0;
-}
 if (!isset($pos)) {
     $pos              = 0;
 }

libraries/export/sql.php

@@ -10,6 +10,13 @@
  */
 $GLOBALS['comment_marker'] = '-- ';
 
+/**
+ * Avoids undefined variables, use NULL so isset() returns false
+ */
+if ( ! isset( $use_backquotes ) ) {
+    $use_backquotes = NULL;
+}
+
 /**
  * Outputs comment
  *