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

Faster version of the function hashing possibly encoded objects, leading to a general speed gain when working with Sets of integers

faster Set loading time from .rdb file resizing the hash table to the right size before loading elements

Fixed VM corruption due to child fclosing the VM file directly or indirectly calling exit(), now replaced with _exit() in all the sensible places. Masked a few signals from IO threads.

Fixed memory human style memory reporting, removed server.usedmemory, now zmalloc_used_memory() is used always.

REDIS_MAX_COMPLETED_JOBS_PROCESSED is now in percentage, not number of jobs. Moved a debugging message a few lines forward as it was called where a few logged parameters where invalid, leading to a crash

fixed a deadlock caused by too much finished processes in queue so that I/O clients writing to the wirte side of the pipe used to awake the main thread where blocking. Then a BGSAVE started waiting for the last active thread to finish, condition impossible because all the I/O threads where blocking on threads. Takes this as a note to myself...

removed support for REDIS_HELGRIND_FRIENDLY since Helgrind 3.5.0 is friendly enough even with many threads created and destroyed

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

Fixed a never experienced, theoretical bug that can actually happen in practice. Basically when a thread is working on a I/O Job we need to wait it to finish before to cancel the Job in vmCancelThreadedIOJob(), otherwise the thread may mess with an object that is being manipulated by the main thread as well.