make loess error-tolerant: Fallback to recal identity or change span.

Added recalibrate.mean and recalibrate.linear (untested)
(fixed missing edits from last commit)
Merge branch 'april2013hackfest' of https://github.com/meowcat/RMassBank into april2013hackfest
Merge branch 'april2013hackfest' of https://github.com/ermueller/RMassBank into april2013hackfest
Merge branch 'april2013hackfest' of https://github.com/ermueller/RMassBank into april2013hackfest