Make SimultaneousFit set errordef correctly automatically from component

[cdeil]

It's nice that the chi^2 and likelihood fit statistics have the default_errordef so the user doesn't have to remember to set Minuit.error_def = 0.5 for likelihood fits.

Would it be possible for SimultaneousFit to look at it's first component and automatically use it's default_errordef.

Maybe it could even look at all components and issue a warning if they don't all have the same default_errordef?