Add thisPackageVersion and notThisPackageVersion

Util functions for makeing dependencies from package identifiers.
thisPackageVersion    (foo-1.0) = foo ==1.0
notThisPackageVersion (foo-1.0) = foo /=1.0
The latter is handy as a constraint in dependency resolution.

Distribution/Package.hs

@@ -46,13 +46,16 @@ module Distribution.Package (
 
         -- * Package dependencies
         Dependency(..),
+        thisPackageVersion,
+        notThisPackageVersion,
 
 	-- * Package classes
 	Package(..), packageName, packageVersion,
 	PackageFixedDeps(..),
   ) where
 
-import Distribution.Version (Version(..), VersionRange(AnyVersion))
+import Distribution.Version
+         ( Version(..), VersionRange(AnyVersion,ThisVersion), notThisVersion )
 
 import Distribution.Text (Text(..))
 import qualified Distribution.Compat.ReadP as Parse
@@ -106,6 +109,14 @@ instance Text Dependency where
              Parse.skipSpaces
              return (Dependency name ver)
 
+thisPackageVersion :: PackageIdentifier -> Dependency
+thisPackageVersion (PackageIdentifier n v) =
+  Dependency n (ThisVersion v)
+
+notThisPackageVersion :: PackageIdentifier -> Dependency
+notThisPackageVersion (PackageIdentifier n v) =
+  Dependency n (notThisVersion v)
+
 -- | Class of things that can be identified by a 'PackageIdentifier'
 --
 -- Types in this class are all notions of a package. This allows us to have