thorough debug trace

*** WARNING: UNTESTED CODE ***

do
    local errorLog = io.open(system.pathForFile("error.log", DocumentsDirectory), 'w')
    if errorLog then
        local function recordLine(event, line)
            errorLog:write(debug.getinfo(2).source, ": ", line, '\n')
            errorLog:flush()
        end
        debug.sethook(recordLine, 'l')
    end
end