d3.median number converting not consistent

[chaosmail]

The number conversion in the d3.median function is not consistent. If there is one number value among other strings, the conversion works as expected. If there are solely numbers as string values, the median string is returned. However, if solely characters are passed to d3.median, undefined is returned.

Here are some examples:

d3.median([2,3,20])
returns 3 as expected
d3.median(["2",3,"20"])
returns 3 as expected
d3.median(["2","3","20"])
returns 20 whereas expected 3
d3.median(["a","b","c"])
returns undefined as expected

[jasondavies]

Thanks! Fix added to #2068.

[mbostock]

Fix staged in #2075 for 3.4.13.