varnishadm -n bla param.set foo -bar

gets interpreted as

	varnishadm -n bla -bar param.set foo

This is counterintuitive and invites random script breaking if people
don't know they have to add an ornamental '--' in front of the CLI command
in Linux systems.

This commit makes Linux work the same way as every other POSIX system.

Fixes	#1496