Process.exit should use "exit" for the message

* Fixes #2632.

Author: eregon

spec/ruby/shared/process/exit.rb

@@ -21,6 +21,12 @@
     end
   end
 
+  it "raises a SystemExit with message 'exit'" do
+    -> { @object.exit }.should raise_error(SystemExit) { |e|
+      e.message.should == "exit"
+    }
+  end
+
   it "tries to convert the passed argument to an Integer using #to_int" do
     obj = mock('5')
     obj.should_receive(:to_int).and_return(5)

src/main/ruby/truffleruby/core/process.rb

@@ -69,8 +69,6 @@ module Constants
 
   FFI = Truffle::FFI
 
-  # Terminate with given status code.
-  #
   def self.exit(code=0)
     case code
     when true
@@ -81,7 +79,7 @@ def self.exit(code=0)
       code = Truffle::Type.coerce_to code, Integer, :to_int
     end
 
-    raise SystemExit, code
+    raise SystemExit.new(code, 'exit')
   end
 
   def self.exit!(code=1)