[development] valid_input_data no more available on 4.6.4

[Gabor Hojtsy]

Karoly Negyesi wrote:
> 
> You can't really do input checking now, valid_input_data was broken
> beyond  repair. We are filtering on output (this was so since long),
> use  check_plain , check_url and check_output as appropriate.
> check_output when  you have a filter format, check_url when you want to
> display a url and  check_plain otherwise if you output your own content.

This important information will end up in some upgrade documentation
right? :)

Goba