Move Redis version detection to utils
Pass test suite against Redis 2.6.x
Sleep more on calculating object idle time

One second isn't enough to let old Redis notice that nothing
happened with the key.
Multiredis travis
Better Redis version detection for test suite

redis-server may not be available for the end users and actually is
required sudo to be executed. However, they have access to redis-cli
which ships with Redis and also provides version info, but in a bit
different format.
travis.yml updated: added matrix to run tests agains redis 2.6
Merge branch '2.6-tests-support'
Closes #50