rhbz460153 - perror should not errcnt across test files

Jacob, folks,

I think the current Dejagnu codebase (4e4eb1534b4) contains a bug
that was initially reported here:

https://bugzilla.redhat.com/show_bug.cgi?id=460153

The bug contains both reproducer and a short patch.  Please,
consider upstreaming it.  Thank you,

Martin