forEachParallel lost input function name information

[leitsubomi]

When forEachParallel expand task function from arguments array , it losts function name, even the task function has name. Please see vasync.js line 135. It will be hard to debug. Please kindly fix it in your convenience.

[davepacheco]

Yeah, this looks to be an artifact of the way we use parallel() to implement forEachParallel().