Fixed problem with sort params in filterLink tag

When filterLink tag was pointing to a different controller than the current, the sort params became invalid. This has been fixed. This change also makes it possible to explicitly set the sort and order parameters as attributes to the filterLink tag.

grails-app/taglib/org/grails/plugin/filterpane/FilterPaneTagLib.groovy

@@ -565,6 +565,10 @@ class FilterPaneTagLib {
      *          The controler that contains the action to use. Optional, default is current controller.
      * @param action
      *          The action to use for filtering. Optional, default is <i>filter</i>.
+     * @param sort
+     *          The attribute to sort upon after filtering
+     * @param order
+     *          The sort order to use after filtering
      * @param *
      *          Additionally you may use all the optional parameters/attrs that you can use to the tag g:link.
      * @body The body of this tag should contain the text to display within the link.
@@ -575,6 +579,9 @@ class FilterPaneTagLib {
         def label = body()
         def controller = attrs.controller
         def action = attrs.action ?: 'filter'
+        // Only copy default search params if it is the same controller    
+        def sort = attrs.sort ?: (controller == "$controllerName" ? params.sort : null)
+        def order = attrs.sort ?: (controller == "$controllerName" ? params.order : null)
 
         def linkParams = [:]
         if (filterParams) {
@@ -586,8 +593,8 @@ class FilterPaneTagLib {
         if (!values instanceof Map) {
             throw new IllegalArgumentException("Mandatory argument 'values' needs to be of type Map.")
         }
-        linkParams.sort = params.sort
-        linkParams.order = params.order
+        linkParams.sort = sort
+        linkParams.order = order
         for (String field : values.keySet()) {
             def value = values[field]