Initial import
Only initialize backend when .htaccess contains authcache fs rules
Extract authcache_fs_symlink and authcache_fs_key_from_keydir functions
Ensure that key-directory is present before a page is saved to the cache
Adapt to new authcache key management API
Support both expire 7.x-1.x and 7.x-2.x
Add requirements check
Merge remote-tracking branch 'upstream/7.x-1.x' into 7.x-1.x