distinguish ghc-7.8.2 from versions before and after

This patch follows the bugfix T9003 of GHC, enabling ghc-events
to distinguish the GHC version that produced the eventlog and
to correctly decode the thread stop status (which was encoded
wrong in ghc-7.8.2). See T9003 for further discussion.
test 782 special treatment (+ test program to gen. traces)