The round() function has issues when trying to do places=1

[sandalle]

In the debug log for 0.3.9, trying to round 99.93125 to one place (we want 99.9):

In round(num=99.93125,places=1), i=4, num=99.9, newNum=, digit=9.
In round(num=99.93125,places=1), i=3, num=99.9, newNum=0, digit=0.9.
Called as round(num=99.93125,places=1), returns "991.90"

While other numbers appear to work:

In round(num=0.6069465,places=3), i=5, num=0.606, newNum=, digit=6.
Called as round(num=0.6069465,places=3), returns "0.607"

-- round() function from
-- http://www.computercraft.info/forums2/index.php?/topic/4023-lua-printformat-with-floating-point-numbers/page__view__findpost__p__31037
local function round(num, places)
    local origNum = num
    num = tostring(num)
    local inc = false

    -- Make sure decimal is a valid integer for later arithmetic
    local decimal = string.find(num, "%.") or 0

    if (num:len() - decimal) <= places then
        printLog("Called as round(num="..origNum..",places="..places.."), already rounded, returns \""..num.."\"")
        return tonumber(num)
    end --already rounded, nothing to do.

    local digit = tonumber(num:sub(decimal + places + 1))
    num = num:sub(1, decimal + places)

    if digit <= 4 then
        printLog("Called as round(num="..origNum..",places="..places.."), no incrementing needed, returns \""..origNum.."\"")
        return tonumber(origNum)
    end --no incrementation needed, return truncated number

    local newNum = ""
    for i=num:len(), 1, -1 do
        digit = tonumber(num:sub(i))

        printLog("In round(num="..origNum..",places="..places.."), i="..i..", num="..num..", newNum="..newNum..", digit="..digit..".")

        if digit == 9 then
            if i > 1 then
                newNum = "0"..newNum
            else
                newNum = "10"..newNum
            end
        elseif digit == nil then
            newNum = "."..newNum
        else
            if i > 1 then
                newNum = num:sub(1,i-1)..(digit + 1)..newNum
            else
                newNum = (digit + 1)..newNum
            end

            printLog("Called as round(num="..origNum..",places="..places.."), returns \""..newNum.."\"")
            return tonumber(newNum) --No more 9s found, so we are done incrementing. Copy remaining digits, then return number.
        end -- if digit == 9 then
    end -- for i=num:len(), 1, -1 do

    printLog("Called as round(num="..origNum..",places="..places.."), returns \""..newNum.."\"")

    return tonumber(newNum)
end -- function round(num, places)