scrypt: 2x faster.

Work on uint32 slices instead of bytes.
Replace usage of Salsa20/8 from salsa package with
the specialized version.

benchmark       old ns/op    new ns/op    delta
BenchmarkKey    266430525    126657130  -52.46%

R=agl
CC=golang-dev
https://golang.org/cl/7139050

scrypt/scrypt_test.go

@@ -17,6 +17,54 @@ type testVector struct {
 }
 
 var good = []testVector{
+	{
+		"password",
+		"salt",
+		2, 10, 10,
+		[]byte{
+			0x48, 0x2c, 0x85, 0x8e, 0x22, 0x90, 0x55, 0xe6, 0x2f,
+			0x41, 0xe0, 0xec, 0x81, 0x9a, 0x5e, 0xe1, 0x8b, 0xdb,
+			0x87, 0x25, 0x1a, 0x53, 0x4f, 0x75, 0xac, 0xd9, 0x5a,
+			0xc5, 0xe5, 0xa, 0xa1, 0x5f,
+		},
+	},
+	{
+		"password",
+		"salt",
+		16, 100, 100,
+		[]byte{
+			0x88, 0xbd, 0x5e, 0xdb, 0x52, 0xd1, 0xdd, 0x0, 0x18,
+			0x87, 0x72, 0xad, 0x36, 0x17, 0x12, 0x90, 0x22, 0x4e,
+			0x74, 0x82, 0x95, 0x25, 0xb1, 0x8d, 0x73, 0x23, 0xa5,
+			0x7f, 0x91, 0x96, 0x3c, 0x37,
+		},
+	},
+	{
+		"this is a long \000 password",
+		"and this is a long \000 salt",
+		16384, 8, 1,
+		[]byte{
+			0xc3, 0xf1, 0x82, 0xee, 0x2d, 0xec, 0x84, 0x6e, 0x70,
+			0xa6, 0x94, 0x2f, 0xb5, 0x29, 0x98, 0x5a, 0x3a, 0x09,
+			0x76, 0x5e, 0xf0, 0x4c, 0x61, 0x29, 0x23, 0xb1, 0x7f,
+			0x18, 0x55, 0x5a, 0x37, 0x07, 0x6d, 0xeb, 0x2b, 0x98,
+			0x30, 0xd6, 0x9d, 0xe5, 0x49, 0x26, 0x51, 0xe4, 0x50,
+			0x6a, 0xe5, 0x77, 0x6d, 0x96, 0xd4, 0x0f, 0x67, 0xaa,
+			0xee, 0x37, 0xe1, 0x77, 0x7b, 0x8a, 0xd5, 0xc3, 0x11,
+			0x14, 0x32, 0xbb, 0x3b, 0x6f, 0x7e, 0x12, 0x64, 0x40,
+			0x18, 0x79, 0xe6, 0x41, 0xae,
+		},
+	},
+	{
+		"p",
+		"s",
+		2, 1, 1,
+		[]byte{
+			0x48, 0xb0, 0xd2, 0xa8, 0xa3, 0x27, 0x26, 0x11, 0x98,
+			0x4c, 0x50, 0xeb, 0xd6, 0x30, 0xaf, 0x52,
+		},
+	},
+
 	{
 		"",
 		"",