change platform to return register names

not just the number of them
also adds protocol to map registers
(like message to r0 , or syscalls)

test/risc/test_platform.rb

@@ -13,8 +13,24 @@ module Risc
       assert_raises{ Platform.for("NotArm")}
     end
     def test_allocate
-      allocator = Platform.new.allocator(FakeCompiler.new)
+      allocator = Platform.for("Interpreter").allocator(FakeCompiler.new)
       assert_equal FakeCompiler , allocator.compiler.class
     end
+    def test_map_message
+      assert_equal :r0 , Platform.new.assign_reg?(:message)
+    end
+    def test_map_sys
+      assert_equal :r0 , Platform.new.assign_reg?(:syscall_1)
+    end
+    def test_map_id
+      assert_nil Platform.new.assign_reg?(:id_some_id)
+    end
+    def test_names_len
+      assert_equal 15 , Platform.new.register_names.length
+    end
+    def test_names_r
+      assert_equal "r" , Platform.new.register_names.first.to_s[0]
+      assert_equal "r" , Platform.new.register_names.last.to_s[0]
+    end
   end
 end

test/risc/test_standard_allocator.rb

@@ -13,11 +13,8 @@ module Risc
     def test_regs
       assert_equal Hash , @allocator.used_regs.class
     end
-    def test_empty
-      assert @allocator.used_regs_empty?
-    end
     def test_reg_names
-      assert_equal 16 , @allocator.reg_names.length
+      assert_equal 15 , @allocator.reg_names.length
     end
     def test_compiler
       assert_equal CallableCompiler , @allocator.compiler.class