Unit tests for parse_common_args()

Add unit tests for most of the basic command line parsing functionality
in parse_common_args(), including the file name handling.

To support these tests, extend arrayref.h to also include ArrayRef,
which provides a mutable wrapper for a C array.  This is complete enough
for the purpose of the tests, but may need additional work for more
general use.  Also fix some documentation typos noticed in the existing
code.

Also, fix unintuitive behavior of etTIME options that was revealed by
the tests.

Change-Id: I4b8b3ad92b0efe24fdf478cd39ba246692b036c7