Cleanup: Corrected link

Corrected link pointing to http://www.icecast.org/svn.php to
point to http://www.icecast.org/download/ as this is what the
webserver now redirects to.

HACKING

 Note that these instructions are *not* necessary for distribution
 tarballs; they have separate configure/build instructions.  
 
-Please visit http://www.icecast.org/svn.php for more detailed
+Please visit http://www.icecast.org/download/ for more detailed
 instructions about building from Subversion.