When running the bootstrapping shell script autogen.sh, no longer set the AUTO{MAKE,CONF}_VERSION env vars. Although these were guarded and only set to default values on OpenBSD if they weren't already set, these should ideally be set by individual users on OpenBSD themselves. Different versions of OpenBSD could well have different versions.

Despite -portable existing to make the codebase compile on platforms other than OpenBSD, there's nothing wrong with making -portable still compile on that platform as well.

Fix some typos. From Christian "naddy" Weisgerber

This adds a 'autogen.sh' wrapper script for generating configure. README.portable is also updated accordingly.