all: fix errors reported by vet, golint

None are "wrong" per se, but there are a lot of good suggestions and
in one case a docstring that was not present in godoc due to the
presence of an extra newline.

Changed "Id" in struct properties to "ID" in some non-exported
structs. Removed a trailing period from some error messages; I believe
the exact contents of error strings are not covered by the Go
compatibility promise.

Change-Id: I7c620582dc247396f72c52d38c909ccc0ec87b83
Reviewed-on: https://go-review.googlesource.com/80145
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

bn256/bn256.go

@@ -49,8 +49,8 @@ func RandomG1(r io.Reader) (*big.Int, *G1, error) {
 	return k, new(G1).ScalarBaseMult(k), nil
 }
 
-func (g *G1) String() string {
-	return "bn256.G1" + g.p.String()
+func (e *G1) String() string {
+	return "bn256.G1" + e.p.String()
 }
 
 // ScalarBaseMult sets e to g*k where g is the generator of the group and
@@ -92,11 +92,11 @@ func (e *G1) Neg(a *G1) *G1 {
 }
 
 // Marshal converts n to a byte slice.
-func (n *G1) Marshal() []byte {
-	n.p.MakeAffine(nil)
+func (e *G1) Marshal() []byte {
+	e.p.MakeAffine(nil)
 
-	xBytes := new(big.Int).Mod(n.p.x, p).Bytes()
-	yBytes := new(big.Int).Mod(n.p.y, p).Bytes()
+	xBytes := new(big.Int).Mod(e.p.x, p).Bytes()
+	yBytes := new(big.Int).Mod(e.p.y, p).Bytes()
 
 	// Each value is a 256-bit number.
 	const numBytes = 256 / 8
@@ -166,8 +166,8 @@ func RandomG2(r io.Reader) (*big.Int, *G2, error) {
 	return k, new(G2).ScalarBaseMult(k), nil
 }
 
-func (g *G2) String() string {
-	return "bn256.G2" + g.p.String()
+func (e *G2) String() string {
+	return "bn256.G2" + e.p.String()
 }
 
 // ScalarBaseMult sets e to g*k where g is the generator of the group and