Make the regalloc module private.

Cretonne clients don't need to know how the register allocator works.

Export the RegDiversions type from the binemit module instead. It is
used by the "test binemit" driver.

lib/cretonne/src/binemit/mod.rs

@@ -6,11 +6,11 @@
 mod relaxation;
 mod memorysink;
 
+pub use regalloc::RegDiversions;
 pub use self::relaxation::relax_branches;
 pub use self::memorysink::{MemoryCodeSink, RelocSink};
 
 use ir::{ExternalName, JumpTable, Function, Inst};
-use regalloc::RegDiversions;
 use std::fmt;
 
 /// Offset in bytes from the beginning of the function.