Issue #2639878 by RobLoach, omega8cc, memtkmcc: Use less demanding check to see if OPcache is active

Issue #2665992 by alexpott, klausi, heykarthikwithu, xjm, tstoeckler: @file is not required for classes, interfaces and traits

Issue #2408533 by markpavlitski: Installation Fatal error: Call to undefined function opcache_invalidate()

Issue #779482 by mikeytown2, sun, cam8001, dalin, segi, alexpott, Sweetchuck, jbrown: Installation failure when opcode cache is enabled.