The symbol is used as the "who" field in the error message.
Also fix lazy-require of runtime-report.rkt in residual.rkt; don't
load until syntax-parse actually needs to produce an error report.
(Previously was loaded to create handler whenever syntax-parse code ran.)
I found I wanted this to make a define/stub macro that errors giving the defined identifier:
(define-syntax (define/stub stx)
(syntax-case stx ()
[(_ header)
(let-values ([(id mk-rhs body) (normalize-definition/mk-rhs stx #'lambda #t #t #f)])
#`(define #,id #,(mk-rhs #`(error '#,id "TODO: stub"))))]))
Closes#508.
Unlike `collapse-module-path`, it makes sense for
`collapse-module-path-index` to convert a relative module path index
to a plain module path. In other words, `collapse-module-path-index`
can convert a module path index to a module path.
