int Ns_ExecArgblk (
Change current directory to
sDir if it is not NULL and executes the file
sExec. All input will come from
fdIn if it's greater than 0; otherwise
stdin will be used. All output will go to
fdOut if it's greater than 0; otherwise
stdout will be used.
argBlk is a string of null-separated arguments, terminated with two nulls, like this: "foo\0bar\0\0".
env is an Ns_Set containing environment variables to pass the program.