* update midnight commander to latest stable release
* refresh subshell patch to support minimal openwrt environment
* switch to sha256 based package fingerprint
* compile & functional tested with ar71xx and x86

Signed-off-by: Dirk Brenken <openwrt@brenken.org>

* backport a slightly modified subshell patch to stable 4.8.15
  (see ticket: https://www.midnight-commander.org/ticket/2742)
* enable subshell support by default

Signed-off-by: Dirk Brenken <dirk@brenken.org>