Make Real.sign always return an Int

Except when the value was NaN, in which case it will return a NaN.
Added candidates for Num (to handle NaN) and Int (to make it almost
2x as fast).

src/core.c/Int.pm6

@@ -51,6 +51,10 @@ my class Int does Real { # declared in BOOTSTRAP
 
     method Int(--> Int) { self }
 
+    method sign(Int:D: --> Int:D) {
+        nqp::isgt_I(self,0) || nqp::neg_i(nqp::islt_I(self,0))
+    }
+
     multi method Str(Int:D: --> Str:D) {
         nqp::p6box_s(nqp::tostr_I(self));
     }

src/core.c/Num.pm6

@@ -31,6 +31,12 @@ my class Num does Real { # declared in BOOTSTRAP
           !! nqp::fromnum_I(nqp::unbox_n(self),Int)
     }
 
+    method sign(Num:D:) {
+        nqp::isnanorinf(self)
+          ?? self == Inf ?? 1 !! self == -Inf ?? -1 !! NaN
+          !! self  > 0   ?? 1 !! self <  0    ?? -1 !! 0
+    }
+
     multi method new() { nqp::box_n(0e0, self) }
     multi method new($n) { nqp::box_n($n.Num, self) }
 

src/core.c/Real.pm6

@@ -3,7 +3,7 @@ my class Complex { ... }
 my role Real does Numeric {
     method Rat(Real:D: Real $epsilon = 1.0e-6) { self.Bridge.Rat($epsilon) }
     method abs()  { self < 0 ?? -self !! self }
-    method sign(Real:D:) { self > 0 ?? 1 !! self < 0 ?? -1 !! +self }
+    method sign(Real:D:) { self > 0 ?? 1 !! self < 0 ?? -1 !! 0 }
     method conj(Real:D:) { self }
     method sqrt() { self.Bridge.sqrt }
     method rand() { self.Bridge.rand }