Added quote-srcloc-string and quote-srcloc-prefix to syntax/location.

Also cleaned up implementation; only generates syntax for requested part(s) of
source location, and is more intelligent about calculation of relative paths.
Abstracted out definition of #%top-interaction, which was copied from
racket/private/pre-base to racket/kernel (and commented as such) in order to
avoid a dependency.  So now it lives in its own module, on which both may
depend.
Copying Dracula implementation from private repository.
Code has been changed just enough for 'raco setup' to run without error.
Testing and certification Makefile ported from private repo.
clarified comment
Moved debug and no-debug into their own collections.
Implemented cond! in racket/cond: like cond, but errors if all clauses fail.