Set dependency to Response when multi in pipeline and build dependency
first if Response's dependency found and not built

* there's some dependency with exec response and command responses
within multi
* if command responses's get() called before exec response's build(), it
calls exec response's build() first
* unit test included
add a number of null check to return methods.

This allows calling these methods on error cleanup paths without having
to surround them with if checks all the time.
Merge branch 'null-check' of github.com:hgschmie/jedis into null-check
Add tests to check returning null to pool
Merge pull request #587 from xetorthio/null-check

add a number of null check to return methods.
Merge pull request #549 from HeartSaVioR/make_multi_in_pipeline_and_sync_work_smoothly

Fix multi in Pipeline and sync() - JedisDataException (fixes #547)
[maven-release-plugin] prepare release jedis-2.4.2
[maven-release-plugin] prepare for next development iteration
revert back version
[maven-release-plugin] prepare release jedis-2.4.2
[maven-release-plugin] prepare for next development iteration