bug#16971: 24.3.50; comment-beginning behaves differently in current newcomment.el, leads to error in comment-indent-new-line

[Dmitry Gutov]

Version: 24.4

Applied (in 116778), but also see 116779.

I've missed some modes that do the same thing, notably lisp-mode and 
perl-mode. Instead of changing them, added a compatibility piece that 
makes those kind of comment-start-skip values work again, too.

Of course, if a mode somewhere checks multiple chars before the 
beginning of a comment, it will still fail.