Declare LocalDiscard and GlobalDiscard (used by kernel/tests/alloc.c)

Declare LocalDiscard and GlobalDiscard (used by kernel/tests/alloc.c)
Remove the DISCARD_DEFINED #ifdefs.
Remove another double HeapFree (caused an assert when run on NT4),
and a HeapSize on a freed heap (the test failed on Win9x).
Fix the LocalLock/LocalUnlock tests (the memory must be allocated
with LMEM_MOVEABLE otherwise the tests don't make sense).
Remove many unnecessary casts.
Improved error reporting somewhat.