fairland: Tweak progress messages

fairland: Tweak progress messages

"fairland: unstable drift -- try increasing DRIFT_MAX" is confusing:
it looks like an error, but isn't, and increasing DRIFT_MAX requires a
recompile.  I'm not sure it can happen.  Replace by just "unstable
drift".

"fairland: error -- continent %c had no room to grow!" is pretty
redundant: it's always followed by "Only managed to grow %d out of %d
sectors."  and then "ERROR: World not large enough to hold
continents".  All it adds is which of the continents failed to grow,
and that's not actionable.  Drop the message.

The message sequence "designating sectors...", "adding resources...",
"setting coastal flags...", and "writing to sectors file..." is a bit
of a lie as these four tasks aren't actually done one after the other.
Replace by just "writing to sectors file..."

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>