Fix for Mantis #23547. Basically we now fail with nicer error messages.

pgenutil.pas:
  generate_specialization:
    + instead of giving an internal error if "symname" is empty and "tt" is "nil" we now do an error recovery by parsing the specialization parameters and returning an errordef (this happens if the "generic" type before the "<" is not found)
    * handle "<>" specially by giving an approbiate error message (both when doing a recovery/parsing a generic and during normal specialization)
  parse_generic_parameters:
    * set the "block_type" to "bt_type" to be on the safe side
    * don't continue with inspecting the def (especially hard typecasting) if the found def is not an "objectdef"

Added tests.

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@23344 3ad0048d-3df7-0310-abae-a5850022a9f2