Fixed median checknan help message

[tinybike]

No description provided.

[ivarne]

We should probably be clare on what happens if checknan=false also?

Also reference the first PR #8602

[simonster]

Does the checknan option even make sense? It doesn't ignore the NaNs; it just gives the median as if they're sorted to the right. Is there a reason someone would want that behavior?

Also, the change to base.rst needs to be in restructured text format, i.e. \" should be double backticks. If you want to update helpdb.jl you should do so by running make -C doc helpdb.jl, although you can also just change base.rst and wait for someone else to update helpdb.jl.

[simonster]

cc @StefanKarpinski since it looks like you first implemented checknan. Is this just a performance optimization to avoid having to check the entire vector for NaNs?

[StefanKarpinski]

Yikes. I don't even remember doing that. But yes, I think it's just a performance optimization.

[simonster]

If I add @inbounds, the cost of the NaN check is about 4%. Is that worth the extra option?

[StefanKarpinski]

Probably not. Just get rid of it.