0.8.12.18: Rearranging COMPILER-ERROR protocol

           * Enhance the protocol to attach the original
                condition and source to the PROGRAM-ERROR.
           * Make compile-time package-lock-violations from
                lexical constructs signal runtime PROGRAM-ERRORS,
                and not drop into debugger during compilation while
                still allowing users to handle them during compilation.
           * While at it, make file compiler errors from undumpable
                constants more informative.
           * Plus a few cosmetic changes to package locking guts.