DATAREDIS-300 - Fix inconsistency with connection open() and close().

Redis connections have been left open when calling RedisTemplate.execute as the connection might have been bound to a thread, released but never been unbound. We now only bind and unbind connections in case of enabled transaction support, while just getting and releasing it for all other purposes.

Original pull request: #69.
DATAREDIS-299 - Assert compatibility with Spring IO.

Upgrade to JUnit 4.11

Upgrade to JUnit 4.11 and remove use of a matcher in an internal
package in favour of the Hamcrest equivalent. To avoid a clash between
JUnit 4.11's Hamcrest dependency and the version of Hamcrest that's
bundled in mockito-all, use of mockito-all has been replaced with
mockito-core.

Fixed deprecation warnings caused by Junit upgrade.

Add and configure the Spring IO plugin such that it's only applied when the
build is run with -PplatformVersion=<version>. This platformVersion
property is used to determine the version of the Platform that will
be used when running the springIoCheck task. The plugin can be used
by running a build as follows:

./gradlew clean springIoCheck -PplatformVersion=1.0.0.BUILD-SNAPSHOT -PJDK7_HOME=… -PJDK8_HOME=…

This will test the project on JDK7 and JDK 8 using the dependencies
defined in the latest snapshot of Spring IO Platform 1.0.0.

Original pull request: #70.