Build and test with only 1.8 or 1.9 mode enabled.

Closes #1558. Closes #1560.

Rakefile

@@ -217,7 +217,7 @@ task :spec20 => %w[build vm:test] do
 end
 
 desc "Run CI in default (configured) mode but do not rebuild on failure"
-task :spec => %w[spec18 spec19]
+task :spec => BUILD_CONFIG[:version_list].map { |v| "spec#{v}" }
 
 desc "Print list of items marked to-do in kernel/ (@todo|TODO)"
 task :todos do

configure

@@ -199,6 +199,7 @@ class Configure
 
     o.on "--enable-version", "VERSION", "Enable Ruby VERSION support (eg 18,19)" do |v|
       @version_list = normalize_versions v
+      @default_version = @version_list.first if @version_list.size == 1
     end
 
     o.doc "\n Compiler settings"

spec/command_line/dash_x_version_spec.rb

@@ -1,19 +1,21 @@
 require File.expand_path('../../spec_helper', __FILE__)
 
 describe "The -Xversion command line option" do
-
-  describe "-X18" do
-    it "sets RUBY_VERSION to 1.8.7 when RBXOPT specifies 1.9.3" do
-      opts = { :args => %Q{-e "puts RUBY_VERSION" 2>&1}, :env => { "RBXOPT" => "-X19" }, :options => "-X18" }
-      ruby_exe(nil, opts).chomp.should == "1.8.7"
+  ruby_version_is ""..."1.9" do
+    describe "-X18" do
+      it "sets RUBY_VERSION to 1.8.7 when RBXOPT specifies 1.9.3" do
+        opts = { :args => %Q{-e "puts RUBY_VERSION" 2>&1}, :env => { "RBXOPT" => "-X19" }, :options => "-X18" }
+        ruby_exe(nil, opts).chomp.should == "1.8.7"
+      end
     end
   end
 
-  describe "-X19" do
-    it "sets RUBY_VERSION to 1.9.3 when RBXOPT specifies 1.8.7" do
-      opts = { :args => %Q{-e "puts RUBY_VERSION" 2>&1}, :env => { "RBXOPT" => "-X18" }, :options => "-X19" }
-      ruby_exe(nil, opts).chomp.should == "1.9.3"
+  ruby_version_is "1.9" do
+    describe "-X19" do
+      it "sets RUBY_VERSION to 1.9.3 when RBXOPT specifies 1.8.7" do
+        opts = { :args => %Q{-e "puts RUBY_VERSION" 2>&1}, :env => { "RBXOPT" => "-X18" }, :options => "-X19" }
+        ruby_exe(nil, opts).chomp.should == "1.9.3"
+      end
     end
   end
-
 end

vm/capi/module.cpp

@@ -30,9 +30,7 @@ extern "C" {
   }
 
   int rb_const_defined_at(VALUE module_handle, ID const_id) {
-    NativeMethodEnvironment* env = NativeMethodEnvironment::get();
-
-    if(LANGUAGE_18_ENABLED(env->state())) {
+    if(LANGUAGE_18_ENABLED(NativeMethodEnvironment::get()->state())) {
       return rb_funcall(module_handle,
           rb_intern("const_defined?"), 1, ID2SYM(const_id));
     } else {

vm/test/test_fixnum.hpp

@@ -1,5 +1,6 @@
 #include "vm/test/test.hpp"
 
+#include "configuration.hpp"
 #include "builtin/exception.hpp"
 #include "builtin/list.hpp"
 
@@ -315,8 +316,13 @@ class TestFixnum : public CxxTest::TestSuite, public VMTest {
     TS_ASSERT_EQUALS(Fixnum::from(-1)->pow(state, Fixnum::from(1)), Fixnum::from(-1));
     TS_ASSERT_EQUALS(Fixnum::from(-1)->pow(state, Fixnum::from(2)), Fixnum::from(1));
     TS_ASSERT_EQUALS(Fixnum::from(7)->pow(state, Fixnum::from(5)), Fixnum::from(16807));
-    check_float(as<Float>(Fixnum::from(100)->pow(state, Fixnum::from(-1))),
-        Float::create(state,.01));
+  }
+
+  void test_pow_with_float() {
+    if(LANGUAGE_18_ENABLED(state)) {
+      check_float(as<Float>(Fixnum::from(100)->pow(state, Fixnum::from(-1))),
+          Float::create(state,.01));
+    }
   }
 
   void test_pow_overflows_to_bignum() {