Modify algorithm of keymap files load:
1) Unconditionally load /usr/share/mc/mc.keymap
2) Unconditionally load /etc/mc/mc.keymap
Then load one of following user-defined keymaps, stop on success:
3) set via --keymap command line option
4) set via MC_KEYMAP environment variable
5) set via keymap key in config file
6) ~/.config/mc/mc.keymap
Fix of double load of keymap file if name is same as name of
system-wide keymap file.
Update man pages.
Signed-off-by: Andrew Borodin <aborodin@vmail.ru>