Update bup split -h output (optspec) to distinguish between split "modes".
Update bup split -h output (optspec) to distinguish between split "modes".

Split it into three lines to clearly show that some modes don't fare
well with others.

Signed-off-by: Gabriel Filion <143a18b53deb6612d517b2e11f8086b561f1df57@lelutin.ca>
[1dc5917c2adeeba13d1ef33dbb40691a1b67cc65@defaultvalue.org: adjust commit message.]
Reviewed-by: Rob Browning <1dc5917c2adeeba13d1ef33dbb40691a1b67cc65@defaultvalue.org>

mhoeher/bup,tjanez/bup,tjanez/bup,pombredanne/bup,tjanez/bup,gevaerts/bup,ToxicFrog/bup,jbaber/bup,jbaber/bup,ToxicFrog/bup,ToxicFrog/bup,pombredanne/bup,jbaber/bup,mhoeher/bup,gevaerts/bup,gevaerts/bup,mhoeher/bup,jbaber/bup,tjanez/bup,pombredanne/bup,ToxicFrog/bup,mhoeher/bup,pombredanne/bup,mhoeher/bup,gevaerts/bup,tjanez/bup,tjanez/bup,pombredanne/bup,pombredanne/bup,jbaber/bup,gevaerts/bup,ToxicFrog/bup,mhoeher/bup,jbaber/bup