[SV 20513] Un-escaped # are not comments in function invocations

[SV 20513] Un-escaped # are not comments in function invocations

* NEWS: Document the change, as a backward-incompatible change.
* main.c (main): Add 'nocomment' to the .FEATURES variable.
* read.c (remove_comments): Skip variable references during remove.
(find_char_unquote): Fix comments for new STOPMAP support.
* tests/scripts/features/escape: Test new escape syntax.
* tests/scripts/functions/guile: Ditto.
* tests/scripts/functions/shell: Ditto.