add bip32: to error messages

...to be consistent with the rest of the library

lib/bip32.js

@@ -35,14 +35,14 @@ BIP32.prototype.fromRandom = function(network) {
 BIP32.prototype.fromString = function(str) {
   var decoded = base58.decode(str);
   if (decoded.length != 82)
-    throw new Error('Not enough data, expected 82 and received ' + decoded.length);
+    throw new Error('bip32: Not enough data, expected 82 and received ' + decoded.length);
   var checksum = decoded.slice(78, 82);
   var bytes = decoded.slice(0, 78);
 
   var hash = Hash.sha256sha256(bytes);
 
   if (hash[0] != checksum[0] || hash[1] != checksum[1] || hash[2] != checksum[2] || hash[3] != checksum[3])
-    throw new Error('Invalid checksum');
+    throw new Error('bip32: Invalid checksum');
 
   if (bytes !== undefined && bytes !== null)
     this.initFromBytes(bytes);
@@ -110,7 +110,7 @@ BIP32.prototype.initFromBytes = function(bytes) {
     this.pubKeyHash = Hash.sha256ripemd160(this.key.pubkey.toBuffer());
     this.hasPrivateKey = false;
   } else {
-    throw new Error('Invalid key');
+    throw new Error('bip32: Invalid key');
   }
 
   this.buildExtendedPublicKey();
@@ -162,7 +162,7 @@ BIP32.prototype.extendedPublicKeyString = function(format) {
   } else if (format === 'hex') {
     return this.extendedPublicKey.toString('hex');;
   } else {
-    throw new Error('bad format');
+    throw new Error('bip32: bad format');
   }
 }
 
@@ -198,7 +198,7 @@ BIP32.prototype.extendedPrivateKeyString = function(format) {
   } else if (format === 'hex') {
     return this.extendedPrivateKey.toString('hex');
   } else {
-    throw new Error('bad format');
+    throw new Error('bip32: bad format');
   }
 }
 
@@ -235,6 +235,9 @@ BIP32.prototype.derive = function(path) {
 }
 
 BIP32.prototype.deriveChild = function(i) {
+  if (typeof i !== 'number')
+    throw new Error('bip32: i must be a number');
+
   var ib = [];
   ib.push((i >> 24) & 0xff);
   ib.push((i >> 16) & 0xff);
@@ -249,7 +252,7 @@ BIP32.prototype.deriveChild = function(i) {
       this.version == constants.testnet.bip32privkey);
 
   if (usePrivate && (!this.hasPrivateKey || !isPrivate))
-    throw new Error('Cannot do private key derivation without private key');
+    throw new Error('bip32: Cannot do private key derivation without private key');
 
   var ret = null;
   if (this.hasPrivateKey) {
@@ -324,7 +327,7 @@ BIP32.prototype.toString = function() {
 
 function uint(f, size) {
   if (f.length < size)
-    throw new Error('not enough data');
+    throw new Error('bip32: not enough data');
   var n = 0;
   for (var i = 0; i < size; i++) {
     n *= 256;