Avoid an issue with virtual functions

Reimplementing virtual functions with
"const &" arguments wasn't behaving as
expected because these arguments were
copied.

Now, "const &" for arguments (in virtual
function reimplementation) is not implemented
as a copy.

In addition, now it's possible to declare
results as references always (also if const &).

See gsiTest.cc:1078 for example:

  //  gsi::arg_make_reference makes the function's return value
  //  always being taken as a reference
  gsi::method<C_P, const CopyDetector &, const CopyDetector &, gsi::arg_make_reference> ("pass_cd_cref_as_ref", &C_P::pass_cd_cref)

testdata/ruby/basic_testcore.rb

@@ -936,6 +936,22 @@ class Basic_TestClass < TestBase
   class C_IMP3 < RBA::C 
   end
 
+  class C_IMP4 < RBA::C
+    def initialize
+      @x = @xx = nil
+    end
+    def x
+      @x
+    end
+    def xx
+      @xx
+    end
+    def vfunc(cd)
+      @x = cd.x
+      @xx = cd.xx
+    end
+  end
+
   def test_19
 
     c0 = RBA::C.new
@@ -978,6 +994,11 @@ class Basic_TestClass < TestBase
     C_IMP2.each { |i| arr.push i }
     assert_equal( arr, [ 0, 1, 2, 3, 4, 5, 6, 0, 0, 1 ] )
 
+    c4 = C_IMP4.new
+    c4.call_vfunc(RBA::CopyDetector::new(17))
+    assert_equal(c4.x, 17)
+    assert_equal(c4.xx, 17)
+
   end
 
   def test_20
@@ -1414,6 +1435,69 @@ class Basic_TestClass < TestBase
 
   end
 
+  def test_29
+    
+    # copy/ref semantics on return
+
+    c = RBA::C::new
+    
+    cd = RBA::CopyDetector::new(42)
+
+    cd2 = c.pass_cd_direct(cd)
+    assert_equal(cd2.x, 42)
+    # two copies: one for return statement and then one for the new object
+    assert_equal(cd2.xx, 44)
+    
+    cd2 = c.pass_cd_cref(cd)
+    assert_equal(cd2.x, 42)
+    assert_equal(cd2.xx, 43)
+    
+    cd2 = c.pass_cd_cref_as_copy(cd)
+    assert_equal(cd2.x, 42)
+    assert_equal(cd2.xx, 43)
+    
+    cd2 = c.pass_cd_cref_as_ref(cd)
+    assert_equal(cd2.x, 42)
+    assert_equal(cd2.xx, 42)
+    
+    cd2 = c.pass_cd_cptr(cd)
+    assert_equal(cd2.x, 42)
+    assert_equal(cd2.xx, 42)
+    
+    cd2 = c.pass_cd_cptr_as_copy(cd)
+    assert_equal(cd2.x, 42)
+    assert_equal(cd2.xx, 43)
+    
+    cd2 = c.pass_cd_cptr_as_ref(cd)
+    assert_equal(cd2.x, 42)
+    assert_equal(cd2.xx, 42)
+    
+    cd2 = c.pass_cd_ptr(cd)
+    assert_equal(cd2.x, 42)
+    assert_equal(cd2.xx, 42)
+    
+    cd2 = c.pass_cd_ptr_as_copy(cd)
+    assert_equal(cd2.x, 42)
+    assert_equal(cd2.xx, 43)
+    
+    cd2 = c.pass_cd_ptr_as_ref(cd)
+    assert_equal(cd2.x, 42)
+    assert_equal(cd2.xx, 42)
+    
+    cd2 = c.pass_cd_ref(cd)
+    assert_equal(cd2.x, 42)
+    assert_equal(cd2.xx, 42)
+    
+    cd2 = c.pass_cd_ref_as_copy(cd)
+    assert_equal(cd2.x, 42)
+    assert_equal(cd2.xx, 43)
+    
+    cd2 = c.pass_cd_ref_as_ref(cd)
+    assert_equal(cd2.x, 42)
+    assert_equal(cd2.xx, 42)
+
+  end
+
   def test_30
 
     # some basic tests for the *Value boxing classes