trace process deaths to the GHC event log
provide a simple API for choosing debug/trace modes
move forever' into Type.hs for general use
trace to the event log *or* to a file handle
cosmetic
tracers are set on startup and immutable thereafter
cosmetic
trace only abnormal process exits
deal with handles explicitly when tracing to a file
document 'trace' primitive for use by users
allow tracing to utilise the built in logger process