http: more descriptive setHeader errors

PR-URL: nodejs#480
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>

lib/_http_outgoing.js

@@ -307,9 +307,9 @@ function storeHeader(self, state, field, value) {
 
 OutgoingMessage.prototype.setHeader = function(name, value) {
   if (typeof name !== 'string')
-    throw new TypeError('"name" should be a string');
+    throw new TypeError('`name` should be a string in setHeader(name, value).');
   if (value === undefined)
-    throw new Error('"name" and "value" are required for setHeader().');
+    throw new Error('`value` required in setHeader("' + name + '", value).');
   if (this._header)
     throw new Error('Can\'t set headers after they are sent.');
 
@@ -327,7 +327,7 @@ OutgoingMessage.prototype.setHeader = function(name, value) {
 
 OutgoingMessage.prototype.getHeader = function(name) {
   if (arguments.length < 1) {
-    throw new Error('`name` is required for getHeader().');
+    throw new Error('`name` is required for getHeader(name).');
   }
 
   if (!this._headers) return;
@@ -339,7 +339,7 @@ OutgoingMessage.prototype.getHeader = function(name) {
 
 OutgoingMessage.prototype.removeHeader = function(name) {
   if (arguments.length < 1) {
-    throw new Error('`name` is required for removeHeader().');
+    throw new Error('`name` is required for removeHeader(name).');
   }
 
   if (this._header) {