Add VersionRange.hashCode.

lib/src/version_range.dart

Index: lib/src/version_range.dart
diff --git a/lib/src/version_range.dart b/lib/src/version_range.dart
index 7020077a7fdfa101051f3122d691dc3bb31efa96..faffb4742335f9d207bc5a86a545a7b925a1405d 100644
--- a/lib/src/version_range.dart
+++ b/lib/src/version_range.dart
@@ -66,6 +66,9 @@ class VersionRange implements VersionConstraint {
            includeMax == other.includeMax;
   }
 
+  int get hashCode => min.hashCode ^ (max.hashCode * 3) ^
+      (includeMin.hashCode * 5) ^ (includeMax.hashCode * 7);

[Bob Nystrom, 2014/10/30 16:45:24]

Idle thought: these multiplications can push the result to a bigint. Do we care
about that?

+
   bool get isEmpty => false;
 
   bool get isAny => min == null && max == null;