pg_database's datpath column must not be marked toastable, because

pg_database's datpath column must not be marked toastable, because
GetRawDatabaseInfo() won't cope with a compressed path spec (much less
a moved-off one).  I'm not going to force an initdb for this change,
because it's noncritical --- we're not actually using datpath at all
right now.  But it seems a good idea to apply the fix while I'm thinking
about it.