Create FSW with filters for relevant extensions

[e9gille]

This is a bit of a hack as it creates a vector of watchers when running on .Net Framework and that may not be what the rest of the Link code expects.

I've gone through the code to check the impact and see a reference ot a QUEUE object that might cause issues, but can't see what is creating it. Apart from that the other places where link.fsw is referenced it should work ok both when fsw is a vector and a scalar object.

[e9gille]

@mkromberg The changes in this PR handle scenarios that are critical at client site and that we would like to see brought into Link v4.0.