[diff -u file from httpd-2.2.6]

Add a new option -r for random URL;
when -r is applied, a URL like [http://www.eachnet.com/search?key={5}] will be randomized to [http://www.eachnet.com/search?key=/* A random string length 5 */ ] in benchmark phase.
This feature is added to eliminate possible bias in results of dynamic sites.

ab之前只支持静态链接的请求，但是就算服务器没缓存操作系统也有缓存，
操作系统没缓存板子上也有L2，所以添加了一个随机选项，开启后每次请求的
字符串不再相同。


Further: 2008/01/15
A randomized benchmark is added the successor of ab - flood.
As far as I know, the new function is added to SVN but not release edition.