C#, D, Java methodmodifiers on destructors

Add support so that the %csmethodmodifiers, %dmethodmodifiers,
%javamethodmodifiers can modify the method modifiers for the destructor wrappers
in the proxy class: dispose, Dispose, delete. With this feature, it is now possible
to make a C# proxy class sealed, eg when wrapping a class X, the virtual method modifiers
can be removed using:

  %typemap(csclassmodifiers) X "public sealed class"
  %csmethodmodifiers X::~X "public /*virtual*/";

Examples/test-suite/common.mk

@@ -170,6 +170,7 @@ CPP_TEST_CASES += \
 	defvalue_constructor \
 	derived_byvalue \
 	derived_nested \
+	destructor_methodmodifiers \
 	destructor_reprotected \
 	director_abstract \
 	director_alternating \