std: Deprecate f{32,64}::consts::PI_2

These constants have been unstable for some time now already

Author: alexcrichton

src/libcore/num/f32.rs

@@ -73,6 +73,7 @@ pub mod consts {
     /// pi * 2.0
     #[unstable(feature = "float_consts",
                reason = "unclear naming convention/usefulness")]
+    #[deprecated(since = "1.2.0", reason = "unclear on usefulness")]
     pub const PI_2: f32 = 6.28318530717958647692528676655900576_f32;
 
     /// pi/2.0

src/libcore/num/f64.rs

@@ -73,6 +73,7 @@ pub mod consts {
     /// pi * 2.0
     #[unstable(feature = "float_consts",
                reason = "unclear naming convention/usefulness")]
+    #[deprecated(since = "1.2.0", reason = "unclear on usefulness")]
     pub const PI_2: f64 = 6.28318530717958647692528676655900576_f64;
 
     /// pi/2.0