Fix for Mantis #25917. With this change the visibility of type parameters is changed from public to strict private as otherwise unexpected (and "unworkaroundable") errors might occur (like the one in the mentioned bug report).

pgenutil.pas:
  * parse_generic_parameters & insert_generic_parameter_types: create the type parameter symbols as strict private instead of public (which is the default visiblity)

* adjusted two tests which relied on this behavior (that's why I fixed the type aliases previously)
+ added test

git-svn-id: trunk@29486 -