crypto/subtle: expand abbreviation to eliminate confusion

Change-Id: I68d66fccf9cc8f7137c92b94820ce7d6f478a185
Reviewed-on: https://go-review.googlesource.com/23310Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/crypto/subtle/constant_time.go

@@ -6,7 +6,7 @@
 // code but require careful thought to use correctly.
 package subtle
 
-// ConstantTimeCompare returns 1 iff the two slices, x
+// ConstantTimeCompare returns 1 if and only if the two slices, x
 // and y, have equal contents. The time taken is a function of the length of
 // the slices and is independent of the contents.
 func ConstantTimeCompare(x, y []byte) int {