rename sql directory to lib-sql

Also introduces a separate constant for the sql directory, so that
it can be put separately from the rest of the data if required.

lib-php/lib.php

@@ -8,6 +8,7 @@ function loadSettings($sProjectDir)
     // set of settings.
     defined('CONST_DataDir') or define('CONST_DataDir', $_SERVER['NOMINATIM_DATADIR']);
     defined('CONST_BinDir') or define('CONST_BinDir', $_SERVER['NOMINATIM_BINDIR']);
+    defined('CONST_SqlDir') or define('CONST_SqlDir', $_SERVER['NOMINATIM_SQLDIR']);
     defined('CONST_Default_ModulePath') or define('CONST_Default_ModulePath', $_SERVER['NOMINATIM_DATABASE_MODULE_SRC_PATH']);
 }