don't use remove() on head in cachedstore's double linked list because of https://issues.scala-lang.org/browse/SI-3970
rename commit to flush for system producer.
tweak kv test to trigger NPE when test is run with Scala 2.8.1. Validate that patch fixes the bug. Add brackets in if else in cached store for style.
Merge branch 'SAMZA-45_NPE-in-linked-list-in-samza-kv-cachedstore'
add mention of SAMZA-45 in cached store comments.