fix error message for applying a non-procedure with keywords
scribble: fix `--redirect{-main}' and non-HTML mode
add `racket/rerequire'

The `dynamic-rerequire' function is the reloading support of
`enter!', but in function form and without namespace-switching.
stepper: ignore submodules

This change keeps the stepper working with the `lazy' language, which
uses the `#%module-begin' from `racket', which in turn now adds a
`configure-runtime' submodule.