GNU Parallel Bug Reports Mixing options --ungroup and --line-buffer gives an error

[Vladimir Kadlec]

Hello,
  when I mix --ungroup a and --line-buffer options, parallel ends up
with an error. I know, it has no sense mixing these two options, but I
think it's a (minor) bug anyway.
I discovered it, because I thought that the --line-buffer option has
to be used with --ungroup (I didn't read the man page carefully).

How to reproduce:
$ ./software/parallel-20151022/src/parallel --version
GNU parallel 20151022

$ ./software/parallel-20151022/src/parallel --pipe --ungroup --line-buffer foo
Can't use an undefined value as a symbol reference at
/home/kada/software/parallel-20151022/src/parallel line 6130.

The version 20141022 is affected too:
$ parallel --version
GNU parallel 20141022

$ parallel --pipe --ungroup --line-buffer foo
Can't use an undefined value as a symbol reference at
/usr/bin/parallel line 5073.

The problem is that in this particular case in $self->{'fd'} for
descriptors 1 and 2 there is no key 'r', there are only keys 'name',
'unlink' and 'w'.

I suggest just die_usage() when these two options are mixed, maybe
with some additional message like 'Can not mix ungroup and line-buffer
options'.

All the best,
Vlada