convert: Use getopt(3)
convert: Add dry-run mode -n
No need for trailing slash here, pkg_old_load_from_path() is adding another
Check return status of pkg_old_load_from_path() and skip if failed
convert: Support using a different pkg_add(1) dir with -d flag
Show converting message before actually processing a package
Export OPTIONS to pkg_install(1) format

Addresses:	#431