Add a modeswitch for type helpers as discussed in core on 24th October 2013. It is disabled by default in all modes (afterall type helper support in Delphi started only beginning with XE3)

+ globtype.pas: add new modeswitch to modeswitch enum and name array
* ptype.pas & pdecobj.pas: check for new modeswitch instead of modeswitch class
* ppu.pas: increase ppu version as we've added a new modeswitch which requires correctly compiled units

* adjusted tests to enabled the modeswitch when necessary
+ added three new tests that check for correct functionality of modeswitch typehelpers


git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@26796 3ad0048d-3df7-0310-abae-a5850022a9f2