Move EntityList and SparseMap into the entity module.

These data structures are dependent on EntityRef and EntityMap, so it
makes sense to keep them in the same module.

lib/cretonne/src/regalloc/solver.rs

@@ -105,10 +105,10 @@
 //! appropriate candidate among the set of live register values, add it as a variable and start
 //! over.
 
+use entity::{SparseMap, SparseMapValue};
 use ir::Value;
 use isa::{RegInfo, RegClass, RegUnit};
 use regalloc::allocatable_set::RegSetIter;
-use sparse_map::{SparseMap, SparseMapValue};
 use std::fmt;
 use super::AllocatableSet;