[Lcdproc] Installation documentation improvement

[Robert Buchholz]

Peter Marschall wrote:
>> I am mostly uncertain about what happens when using USB driven devices,
>> but using --disable-libusb. Don't they work at all or is libusb used
>> anyway?
> 
> configure should warn and not build the drivers.
> See acinclude.m4 how it is done (search for libusb)

But what about CFontzPacket, CwLnx or pyramid? They do not require
libusb, but do they work without it?

Another thing I noticed, is that in acinclude.m4, the way ula200 checks
for libusb is inconsistent with the way IOWarrior handles it.
I am far from an expert in the autotools, but it seems to me that ula200
checks whether libusb is installed whether or not I set --enable-usb
while IOWarrior just checks the flag and doesn't look if libusb is
actually installed (maybe that is done at some other place).


Robert