Correctly handle underscores in CGI param names

Fixes #5

Author: fbbdev

lib/request.js

@@ -74,8 +74,6 @@ function Request(conn, id, role, keepalive) {
 }
 util.inherits(Request, InputStream);
 
-Request.headerExpression = /^HTTP_/;
-
 Request.prototype.close = function() {
   delete this.connection.requests[this.id];
   if (!this.keepalive) this.connection.socket.end();
@@ -85,6 +83,9 @@ Request.prototype.close = function() {
   this.emit('close');
 };
 
+var headerExpr = /^HTTP_/;
+var underscoreExpr = /_/g;
+
 Request.prototype._param = function(name, value) {
   this.cgiParams[name] = value;
 
@@ -95,8 +96,8 @@ Request.prototype._param = function(name, value) {
     if (this._queryString) this.url += '?' + this._queryString;
   }
 
-  if (Request.headerExpression.test(name)) {
-    field = name.slice(5).replace('_', '-').toLowerCase();
+  if (headerExpr.test(name)) {
+    field = name.slice(5).replace(underscoreExpr, '-').toLowerCase();
     if (this.headers[field] === undefined) this.headers[field] = value;
   }