add support for symbolic links for files and directories on Linux boxes

Hello,
I've installed the latest phpAlbum software on my Linux box. By default all photos are placed outside the webserver structure. To prevent unnecessary copies of my photos I created symbolic links to the directories which should be accessible via phpAlbum.
Unfortunately the php code seems to always reference to files and directories (function: file_exists) and doesn't allow to use symbolic links. The phpAlbum code should be able to follow symbolic links (extended by function: is_link) for directories and also for files.

Regards Juergen