Add notThisVersion :: Version -> VersionRange

Opposite of ThisVersion, it means /= x.y but is actually implemented
as > x.y || < x.y as we do not have not or not equal as primitives.

Distribution/Version.hs

@@ -45,7 +45,7 @@ module Distribution.Version (
   Version(..),
 
   -- * Version ranges
-  VersionRange(..), 
+  VersionRange(..), notThisVersion,
   orLaterVersion, orEarlierVersion,
   betweenVersionsInclusive,
   withinRange,
@@ -84,6 +84,9 @@ isAnyVersion :: VersionRange -> Bool
 isAnyVersion AnyVersion = True
 isAnyVersion _ = False
 
+notThisVersion :: Version -> VersionRange
+notThisVersion v = UnionVersionRanges (EarlierVersion v) (LaterVersion v)
+
 orLaterVersion :: Version -> VersionRange
 orLaterVersion   v = UnionVersionRanges (ThisVersion v) (LaterVersion v)