Fix default enum values in help output

Fix default enum values in help output

nenum() does not return an enum value, but an index into the underlying
array, which means that the first element is 1 and not zero like the
code assumed.  The help output was off-by-one, and could error out if
some environment variable was set that was affecting the help output.

Fixes #1438.

Change-Id: Iec2f05c9ced55868902069ce59bc4979a6879f86