fix loader cache
make the cache use a SoftReference
use latest stable release of cascading: 2.5.1
Merge pull request #233 from fs111/master

use latest stable release of cascading: 2.5.1
Merge pull request #240 from Parquet/fix_loader_cache

fix loader cache
upgrade elephant-bird version to 4.3
Merge pull request #242 from Parquet/upgrade_eb_to_4_3

upgrade elephant-bird version to 4.3
[maven-release-plugin] prepare release parquet-1.2.9
[maven-release-plugin] prepare for next development iteration