add Rscons.glob - close #50

build_tests/d/Rsconsfile

@@ -1,3 +1,3 @@
 Rscons::Environment.new(echo: :command) do |env|
-  env.Program("hello-d.exe", Dir["*.d"].sort)
+  env.Program("hello-d.exe", Rscons.glob("*.d"))
 end