fix pretty.names = FALSE in plotThreshVsPerf

[zmjones]

fix for #1167

[larskotthoff]

Could you make the test an additional one please so that pretty names are also tested?

[zmjones]

so i modified a test so that this bug would have caused a failure. you would prefer that i duplicate the test with only pretty.names changed so the failure would be unambiguous? i think the error message would have been easy to diagnose in this case.

[larskotthoff]

Yes. In particular the modified test doesn't test what happens for the other value of pretty names :)

[zmjones]

No but since it is the default it is checked in all of the other calls to plotThreshVsPerf. I don't think in this particular case there is any advantage to duplicating the test since this part of the function is the same across all the other args that are being varied in the rest of the tests.

However the cost to adding another call to the plot function is small, so I can add it if you would really like it :)

[larskotthoff]

Ok, fair enough.