bug#15251: 24.3.50; do-auto-fill "continues" comment from inside a string

[Dmitry Gutov]

On 02.10.2013 03:32, Stefan Monnier wrote:
> - Change code that uses comment-use-global-state to use (and
>    comment-use-syntax comment-use-global-state) instead.

This is already the case: `comment-search-forward' consults the value of 
`comment-use-global-state' only when `comment-use-syntax' is truthy.

> - Maybe make comment-use-global-state obsolete.
>
> Context: the problem with syntax-ppss is not so much performance as
> correctness, because syntax-ppss can get confused if you use several
> syntax-tables in the same buffer (e.g. via font-lock-syntax-table), or
> if you use narrowing.

Yes, that seems hard to test for.

And if `syntax-ppss' can be borked in some modes, using its value in 
`comment-beginning' like I did in the respective patch, also seems unsafe.