Fixing the native Windows file dialog in Rametter-temp-fixes branch

Fixing the native Windows file dialog in Rametter-temp-fixes branch
of GtkRadiant. 	The previous code was Plain Old	Wrong (TM) in the way that
it handled determining which "Save as type" was	selected in the	file save
dialog.  This change affects the function file_dialog() in gtkmisc.cpp.
Fix has	been tested on Windows 7 when the pattern input	parameter is something
such as	"map" and when it's null.  Will	test Windows XP	shortly	and follow
up with	another	commit if it's not working correctly there.

THIS COMMIT SHOULD BE MERGED INTO TRUNK	AT SOME	POINT!!!

git-svn-id: https://zerowing.idsoftware.com/svn/radiant/GtkRadiant/branches/Rambetter-temp-fixes@351 8a3a26a2-13c4-0310-b231-cf6edde360e5