fix(errors) Improve string conversion of errors

When errors get converted to strings in CSV import error dialog, it
 outputs the trace which is way too much text. Errors should convert to
 their error message, to look the same as before we used error objects.

issue #6071

include/errors/class_FusionDirectoryError.inc

@@ -45,6 +45,11 @@ class FusionDirectoryError extends Error
     ];
   }
 
+  public function __toString ()
+  {
+    return $this->getMessage();
+  }
+
   public function computeMsgDialogParameters (): array
   {
     return [_('Error'), $this->htmlMessage, ERROR_DIALOG, static::formatTrace($this)];

include/errors/class_SimplePluginError.inc

@@ -76,6 +76,30 @@ class SimplePluginError extends FusionDirectoryError
     return $array;
   }
 
+  public function __toString ()
+  {
+    $msg = '';
+
+    if (isset($this->object)) {
+      $msg .= $this->object->getBaseObject()->dn.' > ';
+    }
+
+    if (isset($this->tab) && isset($this->tab->parent->by_name[get_class($this->tab)])) {
+      $msg .= $this->tab->parent->by_name[get_class($this->tab)].' > ';
+    }
+
+    if (isset($this->attribute)) {
+      $label = $this->attribute->getLabel();
+      if (empty($label)) {
+        $msg .= $this->attribute->getLdapName();
+      } else {
+        $msg .= $label;
+      }
+    }
+
+    return $msg.': '.$this->getMessage();
+  }
+
   public function computeMsgDialogParameters (): array
   {
     $html = '';

include/simpleplugin/interface_SimpleTab.inc

@@ -135,6 +135,8 @@ interface SimpleTab
 
   /*!
    * \brief Deserialize values
+   *
+   * Returns TRUE or error
    */
   public function deserializeValues (array $values, bool $checkAcl = TRUE);