byobu help screen not shown when $LESS environment contains -F

[Ruben Laguna]

Currently F1 / Shift-F1 will try to open the help page using $BYOBU_PAGER (which can be `less`)

bind-key -n F1 new-window -n help "sh -c '$BYOBU_PAGER $BYOBU_PREFIX/share/doc/byobu/help.tmux.txt'"

If $BYOBU_PAGER is `less` it will load options from the $LESS environment variable, if $LESS contains -F / --quit-if-one-screen, then the pager will exit immediately since the help.tmux.txt file is not that long.

That means that the F1 is unusable in that case since `less` immediately exits, so the user only sees the help page flashed to the screen and immediately cleared.

Proposed solution at https://github.com/dustinkirkland/byobu/pull/64
In order to avoid this $LESS must be cleared inside the F1/Shift-F1

bind-key -n F1 new-window -n help "sh -c 'LESS="" $BYOBU_PAGER $BYOBU_PREFIX/share/doc/byobu/help.tmux.txt'"
bind-key -n S-F1 new-window -n help "sh -c 'LESS="" $BYOBU_PAGER $BYOBU_PREFIX/share/doc/byobu/help.tmux.txt'"