Neither of the optimnization checkboxes were selected on the performance page,...

Neither of the optimnization checkboxes were selected on the performance page, due to data type mismatch. Noticed while testing #113607.

modules/system/system.admin.inc

@@ -1235,7 +1235,7 @@ function system_performance_settings() {
   $form['bandwidth_optimizations']['preprocess_css'] = array(
     '#type' => 'radios',
     '#title' => t('Optimize CSS files'),
-    '#default_value' => variable_get('preprocess_css', 0) && $is_writable,
+    '#default_value' => intval(variable_get('preprocess_css', 0) && $is_writable),
     '#disabled' => !$is_writable,
     '#options' => array(t('Disabled'), t('Enabled')),
     '#description' => t('This option can interfere with theme development and should only be enabled in a production environment.'),
@@ -1243,7 +1243,7 @@ function system_performance_settings() {
   $form['bandwidth_optimizations']['preprocess_js'] = array(
     '#type' => 'radios',
     '#title' => t('Optimize JavaScript files'),
-    '#default_value' => variable_get('preprocess_js', 0) && $is_writable,
+    '#default_value' => intval(variable_get('preprocess_js', 0) && $is_writable),
     '#disabled' => !$is_writable,
     '#options' => array(t('Disabled'), t('Enabled')),
     '#description' => t('This option can interfere with module development and should only be enabled in a production environment.'),