add multi-locale support to iterators in ParallelIO module

[jeremiah-corrado]

Adds multi-locale support to the readLines and readDelimited iterators in the ParallelIO module. If the targetLocales argument is specified, then nTasks tasks will be will be used to iterate over the file on each of the locales. Otherwise, only the calling locale is used (this was the existing behavior).

Example:

var x = 0;
forall line in readLines("file.txt", nTasks=16, targetLocales=Locales)  with (+ reduce x) {
  x += line: int;
}

• [x] paratest