There's extra error codes in #440 for regexes that aren't UNSATISFIABLE
per se, but depend on particular corner cases in PCRE that probably
aren't worth supporting in an automata-based implementation.

Add a test case for one, tests/pcre/in48.re: ^a|$[^x]b*

This is a tricky one to handle properly; according to PCRE it should
match either "a<anything...>" OR "\n", but nothing else. The newline
match is because $ is a non-input-consuming check that evaluation is
either at the end of input, or at a newline immediately before the end.
In this case `$[^x]b*` matches exactly one newline; it's equivalent to
"$\n". This probably isn't worth supporting, but we can detect cases
where a potential newline match appears after a $ and reject them as
an unsupported PCRE behavior.

…-ast-analysis

Ranges using named endpoints are currently rejected with "Unsupported
operator".