Add fix for #114 (#115)

* Reduce code duplication in TypeConstraint subclasses; Add ConstrainWiderOrEqual to ti and to ireduce,{s,u}extend and f{promote,demote}; Fix bug in emitting constraint edges in TypeEnv.dot(); Modify runtime constraint checks to reject match when they encounter overflow

* Rename Constrain types to something shorter; Move lane_bits/lane_counts in subclasses of ValueType; Add wider_or_eq function in rust and python;

lib/cretonne/src/ir/types.rs

@@ -236,6 +236,13 @@ impl Type {
     pub fn index(self) -> usize {
         self.0 as usize
     }
+
+    /// True iff:
+    ///     1) self.lane_count() == other.lane_count() and
+    ///     2) self.lane_bits() >= other.lane_bits()
+    pub fn wider_or_equal(self, other: Type) -> bool {
+        self.lane_count() == other.lane_count() && self.lane_bits() >= other.lane_bits()
+    }
 }
 
 impl Display for Type {