[BUGFIX] Fix clear_cache for XCache < 3.0

The XCache API changed with version 3.0. Ubuntu 12.04 uses XCache
version 1.3.2 so we need to support the old API.

Resolves: #61175
Releases: 6.3, 6.2
Change-Id: I76e975222747c965c5ef6e062231209d398a1c15
Reviewed-on: http://review.typo3.org/32636
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>