HsVersions.h imports and warnings

[Isaac Dupree]

HsVersions.h, included in all source-files, already imports FastString 
(except when COMPILING_FAST_STRING), to make its own SLIT and FSLIT 
macros work.  This generates a lot of "unused import" warnings in 
modules that don't happen to use any of those macros (or "_unused" 
definitions in the modules).  It would only get worse if I added another 
import there.  Any idea how to disable "unused import" warnings from a 
particular import statement and no others, or what else to do about 
this?  I suppose I could add a USE_HSVERSIONS macro that any module can 
use to get rid of all those warnings... which I don't like the sound of, 
much.

~Isaac