Why have file names with 3 components?

[George Russell]

This looks like a bug, but please don't change it!

If you have a file A.blah.hs containing a module A, ghc5.02 compiles it, producing A.hi and A.blah.o.
I have an application for this, since I have just, for the first time, been reluctantly 
compelled to introduce recursive modules.  Rather than writing .hi-boot files (which might have
to be rewritten for ghc5.03) I have instead written .boot.hs files, which yield .hi files, which
then get moved to .hi-boot.   Thus a module A has two sources, the real source A.hs, but also
the source for the .hi-boot file, A.boot.hs.