[fpc-pascal]feature request: enhanced "pos"

[Marco van de Voort]

> >>> x := pos ('Hello', my_str, 6);
> >>
> >> PosEx() from strutils?
> >
> >Cant find it in strutils..
> 
> Just checked the sources again, at least the 1.9.x branch contains a PosEx
> method, line 93ff, from today's sources =)

I implemented some files last weeks in the *utils category.

Not everything is fully tested, so please beware (convutils also exists
since yesterday, but maybe isn't added to all makefiles yet)