Add a parameter to open collapsed fieldsets

When displaying a pieforms fieldset, check the value of the 'fs'
parameter before deciding whether to 'collapse' the fieldset.  This
allows links to be created to (for example) the 'Group settings'
section of site options.

Change-Id: I4e8742d4ed57f1e8b3004fb330f38d6101024dd4
Signed-off-by: Richard Mansfield <richard.mansfield@catalyst.net.nz>

htdocs/lib/pieforms/pieform/elements/fieldset.php

@@ -59,7 +59,7 @@ function pieform_element_fieldset(Pieform $form, $element) {/*{{{*/
                 break;
             }
         }
-        if (!empty($element['collapsed']) && !$error) {
+        if (!empty($element['collapsed']) && !$error && param_alphanumext('fs', null) != $element['name']) {
             $classes[] = 'collapsed';
         }
     }