in code and not in constants. In the case of primitive types constant nodes
are used while complex types like arrays, records and objects use a local
variable which is initialized to zero once at the entry of the method (the
variable is reused if Default() is used for the same type multiple times in
the same method). For this a new compilerproc was added which uses FillChar
to initialize the given memory area to zero.
This fixes Mantis #9420.

+ psystem.pas: Added Default symbol to system unit
+ htypechk.pas: Added function "is_valid_for_default" which checks recursively
                whether the given type can be used with Default at all. 
                Forbidden types are files, helpers, ObjC and C++ types. This
                check is used for records, arrays and objects only if the mode
                is a non-Delphi one, as Delphi ignores these types on lower
                levels.
+ msg/errore.msg: Added error message ...