Run ldconfig on make install as it is required to use the plugins compre...

Fix wrong class name used to print warnings.

This fixes the warnings:

 WARNING: Failed to load plugin module 'compressd': libcompress42.so: cannot open shared object file: No such file or directory

 WARNING: Failed to load plugin module 'zlibvalid': libtinfl.so: cannot open shared object file: No such file or directory

Updated extractor return code to distinguish between non-existent extrators and failed extration attempts.