Required really when writing importers or exports so
only files with the right extention are displayed.

I have tried all sort of things and run up dry gullys
to make this work.
//from memory might be slightly wrong
Blender.window.Fileselector(callback,buttontext)
Now this is the problem I want the users of my import
scripts(me) only to see the files that the import
script can handle. Unless you push the show all button.

As far as I can tell there is no way to peform this
basic tast inside the current python api. This will
make the importers and exports simpler to use. Next
bit is the exportor problem. I am exporting lets say a
3ds file but the Fileselector puts a default of a blend
file in.(yep does not match in hell). Now I have to
write a background correction for safety but it really
should not have to be working all the time. Other
final but verry anoying feature is that I start a New
file inside blender and fileseletor wants to overwrite
my last file I was working on.

Basicly it is a pain in the but that needs fixing.

This also applys to imageselector

A extention of
Fileslector(callback,buttontext,listoftails) and the
first on in the listoftails being the default.