can't start Apache on Mac OS X--no listening sockets available?

[7stud]

Well, I'm able to put html pages in /Library/Apache2/htdocs/ and
access them in Safari as I would expect:

http://localhost/test.htm

and I can access the index.html page in that directory:

http://localhost/index.html

and it displays:

It works! Apache 2.2.4

But, if I just use the address http://localhost/ in Safari, this is
displayed:

It works!

Where is that coming from?  Is the original index.html page(before I
changed it and added "Apache 2.2.4") cached by Safari somehow?  That
doesn't make any sense to me because when I explicitly request
index.html, I get the changed output.