Refactor error messages and Prelude error functions
Refactor error messages and Prelude error functions

- Change from "[debiki_error_<guid>]" to "[error DwE<guid>]"
- Change Prelude error handling functions: require an error code, always
  the first argument (except for any if test parameter) For now, rename
  the functions to "...3", so the complier finds all usages I need to
  update (since changing parameter order)

debiki/debiki-server-old,debiki/debiki-server-old,debiki/debiki-server-old,debiki/debiki-server-old