1.x: concatDelayError with multiple args

[bryant1410]

I think it'd be great if concatDelayError supports multiple parameters as mergeDelayError.

Btw, doesn't mergeDelayError miss a variation in which a variable number of args is admitted?

[bryant1410]

/cc @matir91

[akarnokd]

The general problem with these that they expand the API surface (like + 8 methods per operator) which is already 'bloated'.

We don't do variable arguments in Java 6 because it necessitates @SuppressWarnings almost always (hence the convenience 2-9 arg operators).

[akarnokd]

Closing via #4261.