sort: don't depend on math

No reason to pull in math just for x != x.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/8886043

src/pkg/go/build/deps_test.go

@@ -47,7 +47,7 @@ var pkgDeps = map[string][]string{
 	"math":          {"unsafe"},
 	"math/cmplx":    {"math"},
 	"math/rand":     {"L0", "math"},
-	"sort":          {"math"},
+	"sort":          {},
 	"strconv":       {"L0", "unicode/utf8", "math"},
 	"unicode/utf16": {},
 	"unicode/utf8":  {},

src/pkg/sort/sort.go

@@ -6,8 +6,6 @@
 // collections.
 package sort
 
-import "math"
-
 // A type, typically a collection, that satisfies sort.Interface can be
 // sorted by the routines in this package.  The methods require that the
 // elements of the collection be enumerated by an integer index.
@@ -245,9 +243,14 @@ func (p IntSlice) Sort() { Sort(p) }
 type Float64Slice []float64
 
 func (p Float64Slice) Len() int           { return len(p) }
-func (p Float64Slice) Less(i, j int) bool { return p[i] < p[j] || math.IsNaN(p[i]) && !math.IsNaN(p[j]) }
+func (p Float64Slice) Less(i, j int) bool { return p[i] < p[j] || isNaN(p[i]) && !isNaN(p[j]) }
 func (p Float64Slice) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
 
+// isNaN is a copy of math.IsNaN to avoid a dependency on the math package.
+func isNaN(f float64) bool {
+	return f != f
+}
+
 // Sort is a convenience method.
 func (p Float64Slice) Sort() { Sort(p) }