compiler.cfg.stacks.local: Have unit test load prettyprint implementation for ds-loc so that it always prints as "D 4".
http.server: handle certain parse-errors from the peg vocab

Browsers that can't verify the certificate doesn't send any request at
all which causes parse-errors to be unnecessarily thrown and logged.
peg: add 'got' slot to parse-error, so you get a little more info about why the parsing fails
peg.debugger: don't use formatting.