TWEAK: Only load minify dependencies when the feature is enabled, reducing the risk of conflicts with plugins with obsolete/incompatible library versions.
* FIX: Minify - Make the feature unavailable when W3 Total Cache is active (an ancient version of the library in that plugin is incompatible and can cause a crash if either plugin attempts to perform minification)
* TWEAK: Tweak polling interval for fetching WP-O minify cache information
