multi bulk requests in redis-benchmark, default fsync policy changed to everysec, added a prefix character for DEBUG logs

support for named VM swap file. Fixed a few important interaction issues between the background saving processes and IO threads

Introduced a new log verbosity level, so now DEBUG is really for debugging. Refactored a bit maxmemory. When virtual memory is short in RAM free the objects freelist as well as swapping things out.

LZF compression re-enabled by default, but with INIT_HTAB set to 0 to avoid the very costly memset initialization. Note that with this option set valgrind will output some false positive about lzf_c.c

Changed the reply of BGSAVE and BGREWRITEAOF from +OK to a more meaningful message that makes the user aware of an operation that just started and is not yet finished.

shareobjectspoolsize implemented in reds.conf, in order to control the pool size when object sharing is on