path.extname to behave like basename

[arieljake]

it would be convenient for parsing conventions in filenames if there was an additional parameter to extname like basename of the form ", [ext]".

Example:

var fileName = "index.mobile.html";

path.extname(fileName) // ".html"
path.extname(fileName,".html") // ".mobile

[xavi-]

This functionality should probably be implemented as a module instead of becoming part of core. I believe the powers at be want to keep core as minimal as possible.

[jasnell]

+1 on doing this with a module. I see little benefit to changing this in core.