[m-rev.] for review: Add news about data representation and float boxing changes

[Peter Wang]

Add news about data representation and float boxing changes for 13.05.

NEWS:
	As above.

diff --git a/NEWS b/NEWS
index c2a434a..9cf86f6 100644
--- a/NEWS
+++ b/NEWS
@@ -68,6 +68,21 @@ Changes to the Mercury compiler:
       - large numbers of higher order constructs and/or code that uses
         large hierarchies of type classes
 
+* Consecutive enumeration arguments in discriminated union types can now
+  be packed into a single word to reduce cell sizes, on C back-ends.
+
+* Double-precision `float' constructor arguments are now stored in
+  unboxed form in high-level C grades.
+
+* Double-precision `float' constructor arguments are now stored in
+  unboxed form on 32-bit architectures in the low-level C grade.
+  This was previously so for 64-bit architectures.
+
+* Double-precision float arguments can now be passed via dedicated Mercury
+  abstract machine registers to avoid boxing, in low-level C grades on
+  32-bit architectures. Float variables can occupy two words on the
+  Mercury stack to avoid boxing.
+
 Changes to the Mercury debugger:
 
 * We have added new capabilities to the "level", "retry" and "finish" mdb