Add new method to allow custom validation of content

Author: rastating

lib/wpxf/wordpress/file_download.rb

@@ -68,6 +68,13 @@ def export_path
     File.expand_path normalized_option_value('export_path')
   end
 
+  # Validate the contents of the requested file.
+  # @param [String] the file contents.
+  # @return [Boolean] true if valid.
+  def validate_content(content)
+    true
+  end
+
   # Run the module.
   # @return [Boolean] true if successful.
   def run
@@ -76,7 +83,7 @@ def run
     return false unless super
 
     res = request_file
-    return false unless validate_result(res)
+    return false unless validate_result(res) && validate_content(res.body)
 
     if export_path.nil?
       emit_success "Result: \n#{res.body}"