Symlink support for svn_load_dirs.pl

Patch by Bastiaan Bakker (bastiaan.bakker_at_lifeline.nl).  Adds support for
detecting updated symlinks in svn_load_dirs.pl.  There were no responses to the
latest version of this patch on the dev list.  I've filed it under "tools",
although it's really under the "contrib" directory.

The patch is archived in these locations:
http://svn.haxx.se/dev/archive-2005-02/0611.shtml
http://subversion.tigris.org/servlets/ReadMsg?list=dev&msgNo=92287

http://svn.haxx.se/dev/archive-2005-02/0611.shtml

Original issue reported by mthelen