Use the same order for standard filters as MSVS itself

Recognize the standard "Source", "Header" and "Resource Files" filters
and put them in the same order as that used by MSVS in the project files
it creates.

This avoids gratuitous differences between Premake-generated and the
existing manually created MSVS projects.

modules/vstudio/tests/vc2010/test_filter_ids.lua

@@ -97,12 +97,12 @@
 		prepare()
 		test.capture [[
 <ItemGroup>
-	<Filter Include="Header Files">
-		<UniqueIdentifier>{21EB8090-0D4E-1035-B6D3-48EBA215DCB7}</UniqueIdentifier>
-	</Filter>
 	<Filter Include="Source Files">
 		<UniqueIdentifier>{E9C7FDCE-D52A-8D73-7EB0-C5296AF258F6}</UniqueIdentifier>
 	</Filter>
+	<Filter Include="Header Files">
+		<UniqueIdentifier>{21EB8090-0D4E-1035-B6D3-48EBA215DCB7}</UniqueIdentifier>
+	</Filter>
 </ItemGroup>
 		]]
 	end

modules/vstudio/vs2010_vcxproj_filters.lua

@@ -52,7 +52,32 @@
 --
 
 	function m.uniqueIdentifiers(prj)
-		local tr = project.getsourcetree(prj)
+		-- This map contains the sort key for the known filters.
+		local knownFilters = {
+			['Source Files'] = 1,
+			['Header Files'] = 2,
+			['Resource Files'] = 3,
+		}
+
+		local sortInFilterOrder = function (a,b)
+			if #a.children > 0 or #b.children > 0 then
+				local orderA = knownFilters[a.name] or 999
+				local orderB = knownFilters[b.name] or 999
+				if orderA < orderB then
+					return true
+				end
+				if orderA > orderB then
+					return false
+				end
+				-- This can only happen if both filters are
+				-- unknown, fall back on default comparison.
+			end
+
+			-- Use default order
+			return a.name < b.name
+		end
+
+		local tr = project.getsourcetree(prj, sortInFilterOrder)
 		local contents = p.capture(function()
 			p.push()
 			tree.traverse(tr, {