DistantLand/DistantLandForm.cs -- Remove question mark masks from file s...

This will remove the question marks from the file masks for the Distant Land creation wizard.  This should allow Distant Land to be generated under Wine.  (I cannot test this code personally, since I have no build system for Mono/DotNet.  But once built, I'm willing to give this a shot.)  This is ported from Europop's compatibility work on MGE.