For multichannel mixer controls, add the channel name to each screen
control.
Also make some other small changes.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
The recent ncurses package provides ncurses*-config program to give the
proper cflags and libs. Let's use them if available.
Right now, the ncurses version (5) is hard-coded. It should be better
to be variable as well, but it'd be messy. Hope the ncurses version won't
change rapidly.
