pre-genesis messages tidy-up

Add a new function pretime_message() to avoid bespoke printf in the start up sections of code. Stops silly things like adding a time field to the output before time is created for the odd few messages that use message(). Also add some consist flushes to all these messages so that they stand a better chance of being delivered when an MPI takedown is in progress (that can be very confusing and look like a crash). Finally make sure that the greeting is delivered ahead of any other messages from other ranks so that they do not interleave. Only really an issue when being verbose.

Note based on !1707 (merged) as these changes are also for that, so that should be merged first.