"csdirectorin" "pre:" and "post" code attributes in C# module. Without them it is
not trivial to marshal strings and smart-pointers back and forth
between user callback code and native code. (especially by reference)
Also fixes 2 minor issues in director code generation that are
difficult to come by until "csdirectorin" attribute is extended.
The first is that "ref" types used in directors lead to invalid
signature generation (the type array used to match methods possibly
overloaded by user). typeof(ref T) is used instead of
typeof().MakeByRefType()
The second is that ignored director methods are not completely ignored
- if there was a %typemap(imtype, "directorinattributes") it is not
skipped for ignored method.
