Unnecessary use of FileChannel.force() in Indexed and Block Disk Caches

In: IndexedDisk.write() and BlokDisk.write() at the end FileChannel.force() is called.

It introduces a lot of I/O and affects performance.

After removal of these two lines, mvn test raises no issues.

The test case org.apache.commons.jcs.auxiliary.disk.indexed.HugeQuantityIndDiskCacheLoadTest goes from 450 seconds needed for completion to 30 seconds on my system.

As the data file is useless without proper keyfile, which is stored only on shutdown, then I guess we can resign from fc.force() on data writes.