Hi,

This bug was really annoying me tonight so I wrote the attached patch
which fix it by translating `gv foo.ps&;gv bar.ps&' to `gv foo.ps&gv
bar.ps&'.

I do agree it should be better to provide a way to choice between the
sequential or parallel solution but I have no idea how to implement it
in a clean fashion for now.

Anyway, the current behavior looks buggy and I propose to merge the
attached patch in a first time in order to have a acceptable behavior
that is far better than an error.

Best regards,

Jérémy