* byte-regexp? values should not be considered 3D syntax.
* hash? values are now allowed in serialized syntax properties with (template … #:properties (…))
* marshalling properties which were prefab structs called map on the result of struct->vector, changed it to struct->list as the struct "name" is always serializable.
This change permits EH patterns like (~once <nullable>), because the
match will happen at most once, so there is no danger of divergence.
Thanks to Alex Knauth for pointing out this special case.
Merge to release branch.
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.)
