Add tasks - close #139

build_tests/d/Rsconscript

@@ -2,7 +2,7 @@ configure do
   check_d_compiler "gdc"
 end
 
-build do
+default do
   Environment.new(echo: :command) do |env|
     env.Program("hello-d.exe", glob("*.d"))
   end

build_tests/d/build-ldc2.rb

@@ -2,7 +2,7 @@ configure do
   check_d_compiler "ldc2"
 end
 
-build do
+default do
   Environment.new(echo: :command) do |env|
     env.Program("hello-d.exe", glob("*.d"))
   end

build_tests/d/link_objects.rb

@@ -1,4 +1,4 @@
-build do
+default do
   Environment.new(echo: :command) do |env|
     env.Object("main.o", "main.d")
     env.Object("mod.o", "mod.d")