Hiredis: Advanced async-handling

+ hiredis.c: Convert redisSetError to take format and va_args
+ dict.*   : Fixed generic hash function -> cannot really take signed number
+ async.*  : Valdup function now handles OOM properly
             KeyCompare function uses proper sized integers
             nextArgument - change to use proper str-int conversion function
             Added redisAsyncAppend* function family to support buffer
                                                 optimizations in async-mode
             Added proper error handling on OOM errors [inc buffer rollback]

Review fixes

+ hiredis.c : Reverted back to memcpy(), will test *printf in different time
+ aysnc.c   : Minor changes for better readability

Handle unlikely/pathological OOM conditon cleanly.

More OOM checks