More keybinding fixes

More keybinding fixes
- Fix tiny mode compilation problems
- Fix F-keys not working (silly typo)
- Change file browser to use new backend
- global.c - new helper function sc_seq_or, makes logic simpler down in the functions than calling first_sc_for directly

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@4218 35c25a1d-7b9e-4130-9fde-d3aeb78583b8