Make CDirectory::Exists support use directory cache by default.
Merge pull request #2496 from ulion/check_dir_exists_use_dircache

Make CDirectory::Exists support use directory cache by default.
[GUIInfoManager] Cache the audio/video info for video player labels.
The cache period is one frame (move).
[GUIInfoManager] Cache the audio info for music player labels.
The cache period is one frame (move).