Backport undef-with-in tests from DQ, add "roadwork ahead" exceptions

This is an amalgamation of test changes from 5b67050, 39221d2 and 038b0a7
ilmari++
Clarify in => undef exception (based on 90c87778)
Do not yell loudly on TODOified is_same_* tests
And yet more improvements in the parsing engine

Streamline the construction of -MISC (gah I hate that name) nodes, and make
sure we do not treat placeholders as list element node terminator