Allow loading ?51.dll by hand

-- allow loading ?51.dll files
function modifyPackagePath(postfix)
    local function split(str, sep)
        local sep, fields = sep or ":", {}
        local pattern = string.format("([^%s]+)", sep)
        str:gsub(pattern, function(c) fields[#fields+1] = c end)
        return fields
    end
    local function endsWith(str, pat)
        if #str < #pat then
            return false
        end
        return str:sub(-#pat) == pat
    end

    local additionalpath = ""
    for i, v in ipairs(split(package.cpath, ";")) do
        local newpath = nil
        if endsWith(v, "?.dll") then
            newpath = v:gsub("%?.dll", "") .. "?" .. postfix .. ".dll"
        elseif endsWith(v, "?.so") then
            newpath = v:gsub("%?.so", "") .. "?" .. postfix .. ".so"
        end
        if newpath then
            local duplicated = false
            for i2, v2 in ipairs(split(package.cpath, ";")) do
                if v2 == newpath then
                    duplicated = true
                    break
                end
            end
            if not duplicated then
                additionalpath = additionalpath .. ";" .. newpath
            end
        end
    end
    package.cpath = package.cpath .. additionalpath
end
modifyPackagePath("51")