You want to use wget. Its in nearly all linux distros. On windows, you can get the utility as a part of a a cygwin install, or download the win32 port of common unix utils.
The command to download this is
wget -r -I /repos/asf/incubator/shiro/trunk/ https://svn.apache.org/repos/asf/incubator/shiro/trunk/
This tells wget to get the URL you linked recursively (-r) but only include the specified folder (-I).
wget works in this case because of the simple layout of Apache's svn repository browser. Other svn web interfaces wouldn't allow this to work.
EDIT: If you can ONLY browse with IE, I would guess they're checking the user-agent on outbound requests. Try the following command which mimics IE's user-agent string.
wget -r -U "Mozilla/4.0 (compatible; MSIE 7.0b; Windows NT 6.0)" -I /repos/asf/incubator/shiro/trunk/ https://svn.apache.org/repos/asf/incubator/shiro/trunk/
If this is still blocked by your firewall, then you're probably screwed and will be stuck right-clicking and saving each file manually.