help regarding bug 39445 - writing out tools/

Hi All!

I've been tasked with this easyhack:
https://bugs.freedesktop.org/show_bug.cgi?id=39445

I started with this source, because it seemed easy enough:
http://opengrok.libreoffice.org/xref/core/rsc/source/tools/rsctools.cxx#175

In this source file tools/fsys is only used in this function, and only for
manipulating the extension of a filename in a string. I looked for the sal
equivalent of this, but there doesn't seem to be one. So I thought I'd make
those API improvements the bugreport mentions, but after looking for a good
point in the code to add this file extension changing functionality and not
being able find one, I came to the conclusion that I might be looking in
the wrong place. Tools/ seems like something that was extended as needed,
but sal stands for System Abstraction Layer, and changing the extension of
a filename in a string seems system indepenendent already - I wouldn't want
to clutter the interface of sal with this.

So my question would be: what might be the best place for adding a feature
like this?

Thanks,
Krisztian