Fix Perl tests in OpenBSD regress.

Fix Perl tests in OpenBSD regress.

Disable Perl test t/porting/exec-bit.t as it only checks permissions.
The x-bit in OpenBSD CVS tree does not match Perl distribution tar.
This is known and accepted.

Set permission of Test-Harness source.sh and source_args.sh to
executable as Perl uses it to test module features.  Stay close to
upstream.  During regress, set the x-bit of the files in obj
directory.  Do not touch src tree, it might be read-only.

discussed with anton@; OK afresh1@