* fix for Mantis #38145: allow overloading of assignment operators that return ShortStrings with a specific size
+ added tests

The following rules for using these operator overloads as *implicit* overloads apply (Delphi compatible):
  - if a found assignment operator returns a default ShortString then that is used
  - if only one assignment operator to a String[x] is found then that is used
  - otherwise the assignment is not possible
The explicit assignment checks for an exact match (and falls back for an implicit assignment). This is not entirely Delphi compatible as Delphi seems to favor the first found symbol in that case, but sometimes also not... :/

git-svn-id: trunk@47634 -