SUBSTR is renamed to GETRANGE to have better consistency between command
names (with SETRANGE as its dual). GETRANGE is still aliased as SUBSTR.

HGET HMGET are now COW friendly, plus API refactoring and changes needed for the new implementation.

COW friendly versions of SPOP and SRANDMEMBER commands, with some change to the set encoding-agnostic API.

LRANGE converted into a COW friendly command. Some refactoring, comment, and new addReply*() family function added in the process.

Now the rdbSave* functions return the number of bytes written (or
required to write) in serializing a Redis object, writing to /dev/null
and using ftell (which doesn't work on FreeBSD) isn't needed anymore.

added noeviction policy to redis maxmemory. ZSCORE removed from the list of commands that can't be called when we are low on memory, this command was added in the past for a stupid error.

first attempt to non blocking implementation of slave replication and SYNC bulk data download. Never compiled so far...

Revert "Function to compute RSS memory usage in a fast way, suitable to be called inside keys eviction loops"

This reverts commit 7d47ecd5.

Function to compute RSS memory usage in a fast way, suitable to be called inside keys eviction loops

synchronous I/O networking functions originally used just for replication refactored in a file as generally useful, they are used in the cluster branch for MIGRATE.

Object approximated LRU algorithm enhanced / fixed / refactored. This is used for the VM currently but will soon be used for maxmemory expiring.