add execv - #3

> redis$exec("SMEMBERS hats")
list()
> redis$exec("SADD hats 'big hat'") ## quoting doesn't work
[1] 2
> redis$exec("SMEMBERS hats")
[[1]]
[1] "hat'"

[[2]]
[1] "'big"

> redis$execv(c("SADD", "hats", "little hat")) ## vectorizing does work
[1] 1
> redis$exec("SMEMBERS hats")
[[1]]
[1] "little hat"

[[2]]
[1] "hat'"

[[3]]
[1] "'big"