optimized ini & create

this versions of "init" without the seq expression run 20x faster for me. my comparison:

#time

let createSeq n x = new ResizeArray<_> (seq { for _ in 1 .. n -> x })

let createLoop (n: int) x = 
    let arr = ResizeArray<_>(n)
    for i=0 to n-1 do arr.Add x
    arr

for i=0 to 1000 do  // Real: 00:00:00.506, CPU: 00:00:00.530, GC Gen0: 14, Gen1: 3, Gen2: 3
    let r = createSeq 1000 4.4
    r.Count |> ignore

for i=0 to 1000 do // Real: 00:00:00.016, CPU: 00:00:00.031, GC Gen0: 1, Gen1: 1, Gen2: 1
    let r = createLoop 1000 4.4
    r.Count |> ignore
Merge pull request #264 from gwinsky/patch-1

optimized "init" and "create"