Invalidate Zend OPcache to ensure saved version used

[remicollet]

When using an opcode cache, configuration files are cached.

So, after a configuration file is updated, its old content will be served by cached until invalidated, or checked.

With Zend Opcache, default check delay is 2"

opcache.revalidate_freq=2

And, it is common to have a greater value on production env.

This PR fix this (only for opcache, other opcode caches such as XCache or deprecated APC are not handled)

[slusarz]

This should be abstracted to a common Horde utility class, so that backends other than just Zendf opcode cache will be supported.

[szepeviktor]

@slusarz Could this be implemented in Horde?

[yunosh]

Yes, in the way he explained.