mport permits repository and package mirror fetches over insecure transport

mport is the MidnightBSD Package Manager. Prior to 2.7.8, the mport_fetch_index(), mport_fetch_bootstrap_index(), and mport_fetch_bundle() paths in libmport/fetch.c accepted non-HTTPS repository and package mirror URLs without a url_is_https() enforcement check. When a cleartext URL was configured or returned by mirror data, a network-positioned attacker could tamper with package index or package download traffic and compromise package selection or integrity. This issue is fixed in version 2.7.8.