Update from 2.2.7 to 2.2.8.

<ChangeLog>

• A new form of dict.c (hash table implementation) iterator that performs less copy-on-write of pages, introduced in Redis 2.2.7, caused ZINTERSTORE, ZUNIONSTORE, SINTER, SINTERSTORE commands to behave in the wrong way. This bug is now fixed.
• Print version info before running the test with 'make test'. This is mainly useful for the Continuous Integration system we run.
• Fix for DEBUG DIGEST, key may expire on lookup, producing the wrong result.
• Replication with expire test modified to produce no or less false failures.
• Fixed Z*STORE when dealing with intsets, regression test added.

</ChangeLog>