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This makes things more consistent, and avoids a strange "Prelude is
not loaded" error when there is a Prelude.hs on the search path.

Now not only is if/then a bracketting pair, but then/else is too

If enabled, these accept more layout, but give warnings

It used to break on
    let {x = 'a'} in x
as the 'in' token would keep closing contexts looking for an implicit
'let' layout.

This just ensures that an unsafe coercion is as localised as possible.
For example, instead of
    UnsafeCo (Int -> t1) (Int -> t2)
use 
    Int -> UnsafeCo t1 t2

If we can't derive a type, but it's a reasonable possibility that
newtype deriving would do the job, suggest it. 

A little refactoring too, moving non_iso_class to top level,
and putting it with std_class_via_iso.

If we find ourselves making up an AnyTyCon of kind '??', say, 
then default it to liftedTypeKind.  And similarly for any sub-kind
of LiftedTypeKind.

This is just a tidy-up.

The panic message in ifaceTyConName on IfaceAnyTc 
called the pretty-printer, called ifaceTyConName again,
which caused an infinite regress.  Stupid.

See 
 * Note [The Name of an IfaceAnyTc], and 
 * The Outputable instance for IfaceTyCon

Silences a (harmless) error from tar when making bindists

This works around the two filenames being the same on case-insensitive
file systems.

We define empty datatypes as not being enumerations, which means the
empty blocks aren't generated.

Tracing flags are now:

   -l[flags]  Log events in binary format to the file <program>.eventlog
   -v[flags]  Log events to stderr
              where [flags] can contain:
                 s    scheduler events
                 t    add time stamps (only useful with -v)

and there are more helpful error messages when using flags that are
only available in particular variants of the RTS:

 the flag -v requires the program to be built with -debug
 the flag -Ds requires the program to be built with -debug
 the flag -p requires the program to be built with -prof
 the flag -N requires the program to be built with -threaded
 the flag -v requires the program to be built with -debug

Also, I fixed the crash reported in #3874, with +RTS -ls -v.

We already had a check in configure of the actual build. This patch
adds it to the configure of the bindists too.