added legacy flag to support old range format
Merge pull request #49 from m1keil/master

Patch looks good, thanks for that. One observation:

I have only one observation.. 

Old style perfdata syntax is always negated.. i.e.
5..10 = @5:10 and:
^5..10 = 5:10

So maybe (depending on how pnp4nagios treats the perfdata string) the --legacy option should take care of this as well.