Prevents premature EOFError on blocking reads

[hessammehr]

(rebased) Blocks until the required number of bytes has been read. Only throws EOFError on actual EOF. Fixes #13559.

[pao]

(Rebased version of #13620.)

[vtjnash]

i believe the previous version was designed to be quite significantly more efficient that this replacement. can you comment on the performance?

[tkelman]

If the perf is okay with this version, should remove the unused C function.

[hessammehr]

@vtjnash You are absolutely right.

function bench_readInt64()
       buf = Array{Int64}(100000)
       f = open("/dev/zero", "r")
       for i = 1:100000
              buf[i] = read(f, Int64)
       end
       close(f)
       return buf
end

Before this commit

@time bench_readInt64()

  0.004214 seconds (15 allocations: 782.016 KB)

After

  0.108966 seconds (500.01 k allocations: 31.281 MB, 8.91% gc time)

It seems like readbytes is responsible for some of the performance hit.

@time for i=1:100000 readbytes(a, 8, all=true) end

  0.062285 seconds (300.00 k allocations: 22.888 MB, 6.15% gc time)