A slew of fixes

The attached patch addresses these issues:

• As mentioned by a previous poster, the hard coded paths are undesirable. But the previous version of the patch would not work if clean URLs were enabled. My version uses an absolute path, so clean URLs won't prevent the library from loading.
• In the admin interface, the actual size of the library is displayed, rather than using a hardcoded number. This way, you can upgrade the libraries and have this value update automatically.
• All of the library types are scanned using file_exists(), not just a few.
• Corrected a typo that prevented overlib_mini from producing any output at all.
• Reversed the "title" and "caption" parameters for the two overlib variants, to produce a result that is more consistent with the other libraries.