env.build_after should expand paths - close #35

build_tests/custom_builder/build_after.rb

@@ -3,6 +3,8 @@ Rscons::Environment.new do |env|
               [],
               "CMD" => %w[ruby gen.rb ${_TARGET}],
               "CMD_DESC" => "Generating")
-  env.build_after("#{env.build_root}/program.o", "inc.c")
+  env["build_root"] = env.build_root
+  env["inc_c"] = "inc.c"
+  env.build_after("${build_root}/program.o", "${inc_c}")
   env.Program("program.exe", ["program.c", "inc.c"])
 end