+ call SwapVectors before and after Exec under FPC as well. SwapVectors is
  implemented on two FPC platforms (go32v2 and msdos). On the platforms that
  don't need it, it does nothing, so it's safe to call on all platforms.



git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@28060 3ad0048d-3df7-0310-abae-a5850022a9f2
* limit the heap to 16kb in the i8086 far data memory models for the dos unit
  tests that execute a child process. Otherwise, by default, all DOS memory is
  reserved in these memory models, there's no DOS memory left for the child
  process and exec() fails.



git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@28061 3ad0048d-3df7-0310-abae-a5850022a9f2